How do I get rid of oil sludge?

I recently took my 2005 Kia Sedona to have it's oil changed. It has been about 14000 since the last one(yes, I know that's bad). The place I took it to refused to do it becasue of "sludge" around the filter and on the dipstick. My car is running fine with no noises. One person has told me to use an engine flush and then change the oil, but the guy at Autozone told me not to b/c that could cause even more problems. He told me to change the oil, then change it again after 500-1000 miles. I am really confused as to how to get rid of it. Please advise!!