I'd start by doing a little research, specifically finding out what custom ROMs exist for this model. Not that many Android 4 devices will actually have an Android 9 ROM. I'd visit the xda-developers forum, find the section for that model and see what's there. You'll probably find rooting instructions for that model there as well.

 

Here you go
https://forum.xda-developers.com/galaxy-tab-2

 

Well if I go to the xda-developers forum and type "galaxy tab 2" into their search box it gives me this link to the ROM development forum for that device: https://forum.xda-developers.com/galaxy-tab-2/galaxy-tab-2-unified (which I see I've been beaten to ). At a quick glance I see one Android 7 ROM there, most are Android 6.

 

here you go:
https://androidforums.com/threads/how-to-upgrade-android-version.1314180/

always look to xda for anything root related. it is mainly a developers forum, but i always do my research there for all things root.

main things is to read, then read some more, and then read again.....and if you have any questions please feel free to ask here.

good luck