I am unable to update my watch

Without any other info (watch series, error messages, etc.) see this:

Set up your Apple Watch - Apple Support

FWIW, a lot of people have problems updating a series 3 watch due to insufficient memory. In some cases, unpairing the watch, completely erasing it, then pairing and restoring the backup will resolve the issue after an update. (Simply unpairing and pairing again may not work.)

Unpair and erase your Apple Watch - Apple Support

Also, see fireyjack's reply to:

Can't update her series 3 watch. - Apple Community