Changes

If all has gone well you should be able to turn the gas off and release the pressure in the keg using the pressure relief valve on the keg (usually a small key ring on the top of the keg that you pull to release pressure. You can also let the built up pressure out your tap.

Your keg must first be cleaned, and then sanitized. Normal detergent can be used for normal cleaning, but you cannot use bleach and some other cleaning solutions on them because they are made of stainless steel (which reacts with bleach). I personally prefer Iodophor - which is an iodine based no-rinse sanitizing fluid - Fill the keg up with water and add the recommended amount of Iodophor. Let it sit for a while, then secure the top and flip it over to sanitize the top.