My iPhone 5s sometimes it’s showing no service and sometimes it shows me service And I have updated it to the current version

See these Apple articles below:

If you see No Service, Searching, or SOS on your iPhone or iPad

If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

Manually update your carrier settings on your iPhone or iPad

Manually update your carrier settings on your iPhone or iPad - Apple Support

Update your network provider settings manually on your iPhone or iPad

Update your network provider settings manually on your iPhone or iPad – Apple Support (UK)

If you can't make or receive calls on your iPhone

If you can't make or receive calls on your iPhone - Apple Support