Hard to say without knowing what model of iPad you have
iPad 4th gen - up to date iOS 10.3.4
iPad 5th gen - up to date iOS 16.7.7
iPad 6th gen - up to date iOS 17.4.1
iPad mini 4 - up to date iOS 15.8.2
iPan mini 6 - up to date iOS 17.4.1
etc
Apple have a tendency to not show the correct amount of free space you have
To be sure, you need a large amount of free space, up to 20-25GB
move pictures and video to cloud or other external storage
close all other apps
Again, since I don't know your model of iPad I can't say if your RAM is too small but Apple are not generous with RAM
If your RAM is 1 or 2GB, it is possible that it can not handle the update without deleting every single other app on your iPad
Even a factory reset might not work if the RAM is that small
have you tried a different connection?
if you use a VPN, turn it off
Contact Apple regarding this issue, if you don't want to switch to another device
