How can I upgrade my phone

If you want to update the software, See the instructions in here.

Update your iPhone, iPad, or iPod touch - Apple Support

Since you haven’t posted the model of iPhone that you have, if you check Settings>General>Software Update and you get a message that your software is up to date, then you cannot update any further.

Please explain what you want to do. Do you want to upgrade to a new phone? If so, trade in your current phone for a newer one.