Hi there, @SandRR. Welcome to our Community!
I’m assuming that all your files are currently online, in your Dropbox accounts.
Now, if you delete an account, all its files will be deleted along with it, so it’s best to sift through each account, and decide what you want to keep.
Then, to get those files to the Dropbox account you will be using, you will need to move them over, following the steps shown here.
Once that’s done, you can delete your unwanted accounts.
I hope this makes sense. Let me know what you think, and hold off on deleting anything until we’re sure you have it all backed up!