How do I get rid of an older version of Libre Office that keeps interfering with my newer version?

Hello: I have tried to download newer versions of Libre Office but the old one keeps taking over. Now I have two versions on my computer - the new one (I make new documents with that) and the old one - any existing documents I made before, open with THAT one. It’s very confusing! I want to migrate my older docs into this new version. I do NOT know code. I just want to simply UNinstall the older version.

I have Mac OS10 snow leopard. (yes, it’s almost obsolete; I am poor.)

Some details:
the "new " version I downloaded is Build ID: 3a87456aaa6a95c63eea1c1b3201acedf0751bd5. That is on my desktop.
The “old” one I can’t get rid of is: LibreOffice OOO360m1(Build:3). That is in my applications folder. No matter where I move it to try to delete it, it won’t let me move it to trash because the message says it’s “open.”

When I open an old document made with the old build it comes up in the OLD Libre office. Can I just delete the old application, or do I somehow have to change my hundreds and hundreds of documents made with THAT, to the “new” build - which so far I can only get to open through the internet - and keep from “ejecting” it? (?)

Normally the new program, or whatever, uninstalls the old one, or you have an option to do so. I never received that option and have been fighting with this old build ever since I downloaded it. I don’t want to do anything to old libre office app and risk losing all my old documents. Please, will you help me? I’m not a techie but I can do simple things normally, like install and uninstall applications. THANKS in advance. I just want one - newest - Libre Office build on my computer and I just want all my documents to be OK!

It is necessary to ensure the copy of LO to be removed is not running. Perhaps try restarting the computer and then moving the old version to the rubbish bin.

I would FIRST back up all your old files onto disk or thumb drive (or some other way). Also, before doing anything else, be sure you can reinstall them back onto your computer in a way that they can still be worked with if you need to, and not just “read only” if you don’t want “read only.”