I just purchased the Expansion Pass upgrade for my Witcher 3 game ..

Received an email from GOG saying they had add W3 GOTY edition to my library now as I have purchsed the Game plus the Expansion pass ..

My questions are ..

1. Is there any difference between STD + EXP Pass and the GOTY editions ?

2. Should I uninstall the STD + EXP Pass that I am already using and then re-install the GOTY edition instead ?

1. No, none.
2. There absolutely no need.

The ONLY difference between standard and GOTY is the all-in-one installer.