LG 260 Rumor - erase assigned media?

Okay, so as I use pics and videos for contacts and wallpaper and so on, it gets put in a grouping in the phone's memory called "Assigned Media". In picking a new wallpaper/screensaver, for example, I can choose from those in several locations, such as preloaded, photo album (SD card), or Assigned Media.

If I forget that I've already used a particular pic before and choose it again from my photo album, it adds a new copy of it to my Assigned Media. Even if I remove that item from its assignment and remove it from my SD card, it remains in Assigned Media. The problem is, Assigned Media fills up. And I can't figure out to clean it out.

The phone's very locked-down, lots of options unavailable due to my provider's preferences. The only manuals I've been able to find on the internet are specific to Sprint service in the U.S., and I'm with PC Mobile in Canada, and some menu options are different.

I seem to remember achieving this once before. I know I've had this "Memory full. Delete some itemsfrom In Phone or My Content" thing before (already stupid, because "My Content" isn't what it's called in other places on the phone), and managed to get past it--I think because I was able to remove some old stuff. But now I can't figure out how.

I have the USB link cable, but that doesn't give me access to anything other than the SD card contents.