CAUTION: Only remove one string at a time! Removing all six strings at once dramatically changes the pressure exerted on the neck of the guitar. Relieving this pressure, and then quickly adding this pressure back by putting on a new set of strings can cause some serious problems for your instrument. Best to leave this to the pros.
Be careful with those old electric guitar strings! If left laying around, they can end up in the bottom of your foot, or stuck in your vacuum cleaner. To prevent accidental injury (or a serious repair bill), loosely wrap and immediately dispose of old electric guitar strings.
Take a moment now to clean the newly exposed areas of your guitar with a slightly damp cloth.