Finding difficulties in updating my iPhone

Check compatibility:

Go to Settings/General/About and note the Model Name

• NOTE: iOS 16 is not available for any models except to iOS developers and beta participants. General release will be in Fall, 2022
• iPhone 12 or 13 series: You can update to 15.6
• Any model 6S or newer (including original SE, 2nd and 3rd editions): You can update to 15.6
• iPhone 5S or 6: You cannot update to iOS 13 or higher; you can update only to iOS 12.5.5
• iPhone 5: You can update only to 10.3.4
• iPhone 5C: You can update only to 10.3.3
• iPhone 4S: You can update only to 9.3.6
• iPhone 4: You can update only to 7.1.2

If your phone is eligible for an update see→Update your iPhone, iPad, or iPod touch - Apple Support

If you run into any problems please describe them in detail.

Why not? What happens when you try?

What iPhone model do you have?