I won’t to upgrade my phone now how could I do that

Check compatibility:

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

• iPhone 12 or 13 series: You can update to 15.5
• Any model 6S or newer (including original SE and 2nd and 3rd editions): You can update to 15.5
• 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 compatible, for most users, just go to Settings/General/Software Update or follow Apple's update support article→Update your iPhone, iPad, or iPod touch - Apple Support