HI Jonesy,first welcome to Fishlore , you want to get an aquarium vacuum. LIKE THIS
your local fish shop will definitely have these. you do not want to remove your gravel to clean as this is where some of your live bacteria lives. it will come with some kind of directions. depending on how dirty your gravel is, you will probably need to do a couple times of a period of several days. when you have taken about a 1/3 of the water out then quit for the day. once you get it cleaned then do this on a week to 2 week basis regularly and it will keep it clean.