I gotta stick up for Pete. This is old, but when I look up this phrase, it's a top search result so I want to give people more information. They are both right. It can mean to celebrate and let loose, but it can also mean to "take a load off" or relax and do nothing.... Recline on a chair or put your feet up for resting. Personally, I've never heard of it being used in terms of celebration... except dancing. I do hear it used in the way Pete used it, but this may be because over time the phrase kicking your feet up/kick up your feet got mixed with kick your heels up/kick up your heels.