Resolved Trouble Accessing NAS

I have a NAS with two HDDs. I've mapped them, but now I have trouble accessing them via the mapped designation. I an using Windows 8.1. If I click on one in the File Explorer, I get a device not ready message. I can access them under Network. I thought I might be able to unmap them and start over, but I don't see that as an option when I right click on the mapped drive. I disconnected them, but now I don't see an option to connect them again. I can map them to a new letter, and that works, but I have backup software that uses the the old drive letters and I would like to use those letters.

 

I'm back to the way I wanted. What happened was that I plugged in a USB drive and since I hadn't accessed the mapped drive after rebooting, the USB drive used that drive letter. I noticed that, did an eject on the USB drive and File Manager showed that letter as a removable drive. I opened Disk Management, right clicked on the drive, clicked on Change drive letter and paths. When that window opened, I selected remove. Now everything is back the way I want it to be.