How do i install the version 4.20
you can install it to wherever you like on your pc. Now if you actually meant where can you download 4.20 then you can do that from the epic launcher or from github. from the launcher click unreal engine at the top, then click the library button on the left. you now see a section that says engine versions in the middle area, theres probably a dropdown or something here that will allow you to install the engine. it may list a different version but theres a little arrow next to where it says install, click that and it will show the other versions.