I want to upgrade my iPhone

If you are still on iOS 13 on your phone, you've skipped a lot of updates. The best way to update when you missed a lot of updates is to update using your home computer with iTunes.

See this link for directions --> Update your iPhone, iPad, or iPod touch - Apple Support

And if you still have issues, see this user tip to see if anything applies to you --> Updating iOS: common issues and solutions - Apple Community

What phone to you have and what software version is it on now?