What I can do to upgrade my iOS
How to upgrade my iPhone
Question marked as
What iPhone model do you have exactly?
If you have an iPhone 5s, 6 or 6 Plus, iOS 12.5.2 is as far as you can go at this time. 12.5.2 was just released last week for those models and is up to date for them.
Otherwise, see here: link-> Update your iPhone, iPad, or iPod touch - Apple Support