Hi Ursula,
Glad to be of help. If you've got them backed up already, I'd just make a third copy on a good-quality DVD (i.e. Verbatim) and store it somewhere else (perhaps a friend or relative's place). Then wipe and reuse the SD cards.
I generally transfer my photos off my SDHC/SDXC cards onto the computer and burn them onto two disks (one which is stored at my parents') as well as backing them up onto an external hard disk. The other thing I do is calculate checksums for the photos so that I can tell if the file has been corrupted. I use ExactFile to do this (basically, it computes an almost-unique string of numbers and letters - called a checksum - for each file and if the file changes even slightly, the checksum drastically changes).
