How do you edit keyboard commands?

I would like to know how to edit several keys so that in the game the “w” key makes the player go forwards a set amount when hit, say 256 units, then stop. The opposite direction with the “s” key. I also would like to know how to make the “a” and “d” buttons turn the player 90 degrees left or right.

Ok, let me explain that to you.
In the editor click on Edit->Project Settings and then click input on the left side.
There you can map your input.

Action Mapping is for command-like input (Jump, Shoot,…)
Axis Input is for smoother input like walking, turning, etc.

You can assign a key to a command name and bind the events to a function in SetupPlayerInputComponent function in your Pawn / Character subclass.

There you can use W and S with your CharacterMovementComponent to walk, and A and D with a yaw rotation to turn around. You can find all that below.

If you are a complete starter or want a complete tutorial with examples, look here it helped me a lot: