Hello
I supper new in unreal engine, so my question maybe a little noobish 
How to upgrade unreal engine to new version? I have 4.11.2, and I see that there is a 4.12 version exist.
Do I need to delete engine, and install again?
You should be able to just hit the yellow/orange update button where you can boot up the engine from inside the launcher 
As seen in this picture for example:
No, i don’t have this options
