Is 10 GB of iPhone storage space enough for software update?

Sometimes if you do not have enough free space for an iPhone to update itself wirelessly, you might have enough space to update the iPhone "manually" with the help of a Mac or PC.

Update your iPhone or iPad - Apple Support

Give it a try and you'll find out if you have enough space. If you don't, you can offload things you don't need or use to free up space.