Says not enough iCloud storage available ? Yes I know people with computer does it plug in with lead ?
The computer will need to have the itunes app downloaded on it and yes you use a USB cable.
Save me typing it out and getting explaining itunes app question that may/maynot appear here instructions from apple. Just scroll down to windows computer….
https://support.apple.com/en-gb/HT212156
You could try this yourself…
https://appletoolbox.com/ipad-running-slow-how-to-speed-up-a-slow-ipad/