Can't get rid of old drives

I have installed a new 4tb My book drive and all the software after physically removing an old drive and all the associated software. Using Wdbackup, it wants to use the removed old drive and I have to force it to use the new drive. On the backup screen, I see three drives but only the 4tb drive is plugged in. How can I get rid of the old drives? Also, I have been doing a backup since last evening and only 35% of it is done, is that normal? I am using USB 2 because USB3 has never worked on my PC. Any help would be appreciated. I can understand technical answers like going to the Windows registry if needed.

Problem solved. I removed some old files and folders which were there since 2016. Now I see only one drive unless I plug another one at the same time.