The largest bird ever to fly were the Teratorns (a type of Condor), the largest of which, Argentavis magnificens, had a wingspan of 6 to 8 metres, and weighed 70kg.
The average weight of an adult human is 62kg, which is actually less than that of the Teratorn.
So, a lightweight human in theory could fly. Clearly you would modify the humans not to store large amounts of fat, and for a thinner frame. Bird bones are not actually lighter than human bones as they are denser and stiffer despite being hollow. You would somehow need to remove the weight of the wings and other adaptions from the rest of the body to keep the weight constant as you add flight capability.
Other adaptations made in birds that would most likely be needed in your humans are:
- A deep, solid breastbone (sternum) to which the wing muscles can be anchored.
- Get rid of un-needed bones. For example fewer fingers, thinner skulls, etc.
- Keep reproductive organs tiny most of the time, have a breeding season.
- Much larger more efficient lungs (continuous flow)
- A more powerful heart and increased blood flow to the wing muscles
The most visible change needed though would be the six meter wingspan. Each arm would need to be 3 meters long. In other words the arm would extend from their shoulder and the elbow would nearly reach the floor, and then the forearm would extend back up the same distance to place their hand by their shoulder. Even folded up this would be a massive deal, and would greatly limit them in their daily lives.
The wrist may well need to be elongated as well to give the wings 3 points of articulation, which would mean the first two bones would not need to be so long but the hand becomes even less flexible and useful.
While they would have no problem reaching top shelves they would have to be constantly folding their arms and find most areas designed for normal humans incredibly claustrophobic. All furniture and living areas would need to be designed especially for their use or be uncomfortable. In particular they would struggle to reach or do anything close to them, preferring to actually be a distance from anything they are working with.
So in conclusion, your flying humans would have enormously over-long arms and clumsy few-fingered hands. They would have large massively muscled and protruding chests and thin fragile skulls.
But they would fly.