My phone model is iPhone 7 but the software version is only 13.61. How do I update it? Only IOS 14 update?

With you operating system being that old, you will most likely need to update using a computer.

Update your iPhone, iPad, or iPod touch

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.5

• If you have an iPhone 6S through 13, you can update to 15.4.1

Go to Settings > General > Software Update.

Update your iPhone, iPad, or iPod touch using WiFi -

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

Update using your computer -

Update iOS on iPhone - Apple Support