You can switch to sand, I would do it 50% at a time though, as substrate can house a decent amount of nitrifying bacteria and you really don't want to start a mini-cycle.
How to clean it:
Get a clean 5 gallon bucket. Pour the sand into it until it is 1/3-1/2 full. Then put a hose into the bucket, turn it on, and churn the sand. Churn, churn, churn. If you think it might be clean, turn off the hose, and allow 30 sec.-1 min. to see if it will settle. If you can clearly see the sand clean it again for about 5 more min. If it doesn't settle you have to clean a lot more.
In the aquarium:
Instead of digging the siphon head into the substrate like you do with gravel, hold the siphon about 1/2-1 inch above the sand and it should pick up the fish waste and other stuff from the sand. If you have a weak siphon like me, you can let it virtually touch the sand and it won't suck any sand up. Some people churn the sand every month in the aquarium to make sure no poisonous gas pockets are developing, but others say this is unnecessary.
As for the filter, look at the filter instruction manual. I know in the tetra whisper filter manual it says specifically, "Do not use in aquariums with sand." You'll just have to look, although most filters are sand-friendly.