The yellow wall should be changed. They do not complement the other finishes.

Once the walls are repainted please select a more modern light fixture. Your currnet one is not nearly large enough and is hung way too high in the room.

Once those tasks are accomplished, you might not think the staircase railing needs to be made more modern. I might consider painting the stair risers white to contrast the wood like you see in the picture below.

Thank you, yes, the paint needs to be refreshed for sure.

I wouldn't add a metal handrail but leave the balusters. Either just paint the handrail or replace everything--handrail and balusters. Depends on your budget--replacing everything is going to be quite expensive. Bev's third photo showing before and after would be easiest to do.