Replacing the rear wheel is a simple task, although the gear mechanism makes it a slightly more complicated than replacing the front wheel.
If the bike has a horizontal slot for the back rear wheel you will need to adjust the rear wheel carefully by to get it in the best place.
Tighten The Fixings
Check the position of any washers and tighten the nuts on each side by hand. Use the spanner to half-tighten each nut in turn. Check the rear wheel is still centred then fully tighten each side in turn.
Close the brakes
Close the brakes and check they’re working well