Install disk from 3.1 have an "upgrade" button to upgrade the OS you are using. Don't remember if it allow to upgrade from ancient WB2.x.
But it will surely overwrite your preferences, startup-sequence and user-startup. Making a backup of those archives will not hurt you.
But as
stefcep2 wrote, get Classic Workbench. It will give you a completely installed Workbench with all needed features you need.
The Green Amiga Alien Edition (R.I.P. Paul, you'll be not forgotten) is a must for OCS/ECS machines and will
fly on an A2000. Regular versions are more intended for AGA systems.
MCP is another
great program, it saves you from hunting a lot of minor patches, functionalities and enhancements.
Also OS3.9 is OK (but not stunning fast) in a decently expanded A2000 (030 @33MHz or better) with at least 6Mb of RAM. More RAM the merrier, of course. Over 12Mb (4Mb of Zorro2 and 8Mb 32bit RAM) is more than perfect for 3.1.
My A2000 have OS3.9 (with
legal 3.1 ROM) and I'm satisfied with this beast.:mickeymouse: