Method 1 ( Recommended ):
You can use a plugin named "Envato Market" for auto update and here's a tutorial how to do it :
https://envato.com/market-plugin/
Method 2 :
Note : Don't worry you won't lose the Youzify settings on updates ^^
1. Deactivate the old version.
2. Remove the old version.
3. Install the new version.