I am unable to update my iOS 14. What am I doing wrong?

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

https://support.apple.com/en-in/HT204204

If your iPhone, iPad or iPod touch won’t update

https://support.apple.com/en-us/HT201435

What version of iPhone do you have? If it supports iOS 14, it would support the latest iOS which is 15.2. If your phone can be updated, it would update to the latest version unless you are seeing an error. If you are seeing an error, please report that error.