I think a little more information is in order. What makes you say that the campaign is not going well? Is it a question of perception or have the players told you as much? I have found, reading these boards, that a lot of new DMs percieve their early attempts to be utter falilures while they might be OK (not complete successes, but OK).
You say you want to change campaings. There are no complete and downloadable campaigns that I know of. Most campaigns I know of are the result of a combination of self-written adventures and published ones. You might get lucky, however I must point out that a very common reason for campaigns to crash and burn is a problem of expectations. If your players are looking for a fight (ie the typical door-monster-treasure) type of game and you are running a deep political intrigue, players are sure to be disapointed and the campaign is doomed for failure. Therefor my third and fourth questions are : What type of campaign are you running (The Sunless Citadel is a dungeon crawl that can turn into the classic aformentioned door-monster-treasure adventure quickly)? Is this the type of campaign the players were expecting?
That is it for now,
Guillaume