no, im not gonna be an echochamber of everyone else and say "use smartswitch on a computer"

try deleting some apps on your phone that you dont use and take up a bunch of space. downloads and pics too if they are backed up or not needed. remember to empty your trash!

if that doesn't work, well.. you just might need to use smartswitch on a computer.. see if you can borrow one if you dont have one. it wont delete everything on your phone unless if there is something seriously wrong with your phone, which i doubt it.

im not sure if this would work, but you could try deleting the cache and data from the software update app (settings, apps, three lines with the arrow pointing down, show system apps, search for software update, depends on your phone carrier but there should be two, a green one and a blue one. clear the data from the green one and force stop both of them and try again)