Hi there!
I got one question about the W3 GOTY Edition, i got W3 installed on my pc from DVD's but i wanted to play the expansion pack so i bought it week ago in gog.com and automaticly my Witcher 3 changed in GOTY Edition, so my question is do i have to download all files of GOTY Edition to play Hearts of stone and Blood and wine? It would be quite problematic for me coz my internet connection is not so fast :(

No. The GOTY edition is exactly the same game as the base game plus all DLCs and expansions. The only difference is that the GOTY comes all-in-one, with a single installer. Just install the expansions, but make sure your game is up to date first: the expansions *require* it.

But which files i have to download from GOTY Edition? Is it part 9 and part 10? Those are expansions?

Go to your account (web, NOT Galaxy) and select TW3. You will see 'DLC Downloads'. Hearts of Stone is two parts, Blood and Wine is three parts.

Edit: you CANNOT download the expansions alone from the GOTY, that is all-in-one. The files you require are the files you bought from GOG, NOT the GOTY.

So in the end i have to download all files from GOTY Edition? I dont have single expansions in library.

No, you don't. You said that you bought the expansion pass at GOG. If that is the case, it will be in your account, and you can download it from there. You do NOT have to download the entire GOTY just for the expansions.

But there is no single expansions in my library atleast i can't see them, there is only GOTY Edition and that's it. When i bought W3 i registered it on this account and after buying Expansion Pack it changed into GOTY Edition.

EDIT: Nevermind, I just found it, I had in my library W3 as you said, thanks for help man :)