How the newcomers will be greeted depends on a number of variables.
State of the Colony
Is the colony living hand-to-mouth, or are they living in the lap of luxury?
If only a few decades have passed then chances are that the colony is still not too well off. The arrival of a colony ship stocked full of seeds, food rations, new equipment, spare parts, etc. would be seen as a massive boon.
In this case the space-travelers would probably be greeted with open arms.
If, however, they have a really good infrastructure/economy set up, but limited resources (such as not too much inhabitable land), and a few thousand new settles show up then that wouldn't really "work" for the colonists.
Colonist Culture, Political Ideology
How far removed from the original colonists are the people living on the planet? If they are in fact the same people who climbed aboard a colony vessel on Earth then they will share a deep bond with the people now arriving: they will have endured the same dangers of crossing interstellar space, and the same hope of starting new lives on a different planet.
In this case the two groups will be able to relate to on another. Furthermore, if the history of such groups meeting is to share resources freely then things will most likely go relatively smoothly.
However, imagine if the history of such arrivals is for the stronger group to simply enslave the weaker one. For example for the colonists to either seize the ship and use the new-comers as slave labor, or for the colonists, arriving with superior technology, to supplant the colony government and impose their own rules (imagine a new religion developing on Earth and sending out zealots to forcibly convert existing colonies).
Another scenario is that once arrived on the planet the colonists fall into anarchy, and the arriving ship finds an unstable political situation, with various groups claiming to be "the good guys", while they all secretly want to rob the travelers of their gear and enslave them.
The possibilities and their implications are too many to list.
If the colonists are several generations removed from the original settlers then the tech of the new-comers will probably be far more advanced than anything that could be found on the colony.
The new-comers could at that point offer their technology in trade, or simply use their might to crush the locals into submission.
Alternatively, maybe the original colonists counted some brilliant scientists among them, who developed tech which no one on Earth had ever even imagined. For example maybe the colonists form a culture of genetically modifying themselves in order to adapt to their planet, rather than terraforming it.
Maybe they find alien artifacts which mutates them, enslaves them, or allows them access to a hoard of tech of unparalleled power, but which they wish to keep absolutely secret because of its destructive potential. Again, there are countless scenarios.
When the seed ship arrives will they be absolutely shocked by the lifestyle that the colonists have embraced? Will they find a group of infected, alien-artifact-enslaved monsters like in Dead Space (the video-game)?
This question is too freakin' broad!!!
"Songs of Distant Earth" by Arthur C. Clarke
I read a novel some years ago that dealt with a similar scenario.
--- Spoilers Ahead! ---
A colony had been established on a gorgeous planet some centuries before. Being very far from Earth, they did not communicate with their home-world.
In the mean-time, a cataclysmic event causes a massive extinction event on Earth. In a last desperate bid to ensure the survival of mankind "seed ships" are launched into the void of space, hoping that the colonization of as many worlds as possible will ensure the future survival of mankind.
One such ship - which had been on its way to another world - finds itself heavily damaged by a meteor impact, and has to stop and replenish supplies on this world, which they weren't even certain still hosted a surviving colony.
They arrive with technology far more advanced than what the colonists have available. They run into language barriers, and more importantly, there are diseases which one group is impervious to, but have severe effects to the others.
Emotions run high. Many of the crew don't want to continue their perilous journey now that they know this colony is habitable, while others see it as their mission to go further and settle yet another world in order to ensure that mankind is as "spread out" in the universe as possible.
At the same time the natives are feeling exploited because they have to allow access to these outsiders to all sorts of resources that they could have extracted and used themselves.
In the mean time political leaders on both sides share the knowledge that if they really wanted to, the space-travelers have the weapons and gear to take anything they wish.
The space travelers end up deciding that continuing their journey is for the best, however your situation ends in the exact opposite way.