This question already has an answer here:
I have a 4 GB drive with Time Machine backups on it that I've not used in a couple of years. It's nearly full. I wanted to start using it again, but first I wanted to remove ~2/3 of the backups, to free up space, while keeping a good sampling. Thus I removed 50 of the 70 backups (cmd-delete in Finder), alternating removing two and keeping one while going through the entire list chronologically; as a consequence, what remains goes back just as far, just with less frequency.
But, after doing this, the drive is still nearly full. I figured that's because I needed to empty the trash, but when I tried to do that it removed items slowly, and then stopped. So I stopped the emptying and checked trash, and saw nearly nothing had been removed. I then ejected the drive, after which the trash was empty. But when I re-mounted the drive, the items in trash all reappeared.
There is a procedure given in this thread, but the behavior the OP describes doesn't exactly correspond to what I'm seeing: How can I manually delete old backups to free space for Time Machine?
So: Should I try the terminal command in the above thread? Or do the problems I'm having indicate my Time Machine partition may be corrupted? If the latter is the case, it would make the most sense to just reformat the disk and start clean. Granted, it would be nice to have some of the old backups, but I don't have a critical need for them (not critical enough to buy a new disk and put this one in storage).
UPDATE: Never mind. I tried adapting the instructions given in the post Allan linked, and couldn't get them to work. So I just erased & reformatted the entire disk and started over. In retrospect, my mistake was following an answer I found elsewhere on apple.stackexchange.com, which said one could delete individual backups in Finder by dragging them to the Trash. I should have instead used tmutil in Terminal.