I just bought the expansion pass and when i was about to install it it said my game version was too old, that i needed the latest patch. Found out that I haven't updated my game a single time and is at patch 1.08. Can someone please explain how I can download the latest patch.

Try these steps (if you install the witcher with gog launcher):

1. Copy "The Witcher 3" folder to desktop and rename the folder to this 1207664643, but its better you check the game number self :

- go to D:\Program Files (x86)\GalaxyClient\Games\The Witcher 3 Wild Hunt (or where your game is) and open the "goglog.ini", in the first line is a number, rename the folder with your number, without [ ]

2. deinstall The Witcher with the gog launcher
3. Copy the folder in the temp folder , Then right click on the folder and remove the point by read only

D:\Program Files (x86)\GalaxyClient\Games\!Downloads\temp (use your download path)

4. install now the witcher with the goglauncher, the launcher should check now the files in the folder this need a lot of time! When they is ready, they should dowlnload only all files be missing ( for example: 30 GB from 45 GB)!

If you own all expansions on GOG.com then you will be gifted the GOTY edition -- check your account (web, not Galaxy). Uninstall your current game, download the GOTY and install.