ID:2558395
 
(See the best response by Lummox JR.)
So I've been trying for like a half a day now and I've restarted and shut down my computer multiple times, but I've attempted to download (even uninstall Byond to see if it would work) Byond 513 from the pager or Byond source only to be met with this message.

https://prnt.sc/rszmyh

I don't know how to stop it cause it won't let me download the latest version of byond so I might need some help.
You have either Dreemseaker, Dreamdaemon, or Dreammaker open, close all BYOND programs to continue the installation.

If you keep clicking 'ok' it will ask you if you would like to 'kill' the running byond processes. Click 'kill' and it should work.
Yeah, I did that. It still for some reason gave me that message, I tried to do so after shutting down my laptop and trying again. I don't exactly know what I have open still that's causing that message cause I've even checked task manager to see if something was still running that I didn't notice.
Have you tried manually deleting the BYOND folder?
No I have not, let me attempt.

--EDIT--

After I had deleted the Byond folder (I assume the one in documents) it still hasn't let me download the latest version of Byond.
To preference it's also saying that Dream Seeker is still running despite the fact I believe it's closed.
Best response
In Task Manager, are you checking the details tab? That will show you the actual programs running whereas the processes tab just shows you programs that have windows open. It's a subtle but very important difference. Personally I never use the processes tab for that reason.