How do I change lights bulbs that are 20 feet off the ground and pointing up (in a vanity fixture)?
If you don't want to get an 20' extension ladder (which can be very difficult to transport home from the store), then you can get one of the  Little Giant or Werner multi-ladders:



Or you can get the werner folding ladder:



But, a good ladder will pay off in more ways than just this - cleaning gutters, etc.