I cant update my Apple Watch

Without knowing anything else (series, iPhone model, iOS & watchOS version, etc.) perhaps one of these articles will help:

If you see "Unable to install update" when trying to update Apple Watch Series 1 or Series 2 - Apple Support

Update your Apple Watch - Apple Support

Unable to Update Watch - Apple Community'

What model of phone is it?.

Which model of watch is it?.

Which version of ios is on the phone?

Which version of watchOS it the watch running?

What error messages are you receiving?

A bit more info please.