How do I clean the filter in my tank?

I need to clean the filter in my goldfish tank and change the filter pad, but I'm not sure how to do this because the filter is being weird. The power went out once and when it turned back on, the filter had slime stuff coming out of it. It's just hanging there. I know, that means it's over dirty! It happened because I missed a week of cleaning it, my stupid siphon isn't working right and that week was when I was supposed to change the filter pad too….anyway!
How do I go about cleaning this?
Thannk yooouu. :]