Fill them with more
juice! Of course you will have to
buy some, but that's about all you can do. When they are done to the point of yick, they can often be cleaned (Soak in vodka over night, flush with hot water a lot, dry in 250 deg oven for 30 min). They should come out pretty good after that and can be filled again. If they clog and it doesn't clean out, you might need to do something like this:
http://www.e-cigarette-forum.com/fo...clogging-boge-cartos-sharp-needle-method.html
My cartos last for weeks, but I don't use prefilled ones. Cheaper and better to
buy blanks and buy your own juices...or even make them yourself! But that is another topic entirely.