SD card of 1GB Full after 260 MB

I have two r4 cards (2years old) with 1GB memory, one of those cards is full after 260 MB. On the other card there is over 850 MB installed games?How can I really "clean" the memory? I just deleted the old games.

you might not be able to, the missing space could be worn out.

Thanks for helping! I''ll just buy a new card. Think that's the easiest solution.
Again many thanks, this forum is great to find solutions and helped me already a lot!!

Did you try formatting?

No, how do I do that? A very long time ago I knew how to format a diskette... But that was in 1986 ???

Insert SD card in reader, right click on it in explorer and choose "Format". Chances are it won't help if deleting didn't, but it's worth a shot.