When your friends just want to party it can be hard, but you basically have to options: Option 1: Get new friends, Option 2: talk to your friends and see if they will change.

Option 1: get new friends. It is not easy to go find new friends, but the fact is if every time you are with your friends they only want to go out and party, and you don't it might be the best to move on to new friends, and still hang out with the old here and there, but not spend your life unhappy. So, look for new friends that have similar interests as you. Look for friends that will want to do something other than party. If these are the kinds of friends you want to have, you can't go to bars to meet them. Start by looking for friends in activities that you are already involved in and enjoy. Maybe get to know someone that is in your workout class at the gym, or in your office, or who lives in your neighborhood.

Option 2: Talk to your friends. Sometimes the best way to deal with friends who party too much is to tell your friends how you feel. You want to tell them that you love being their friend, and that you want to spend time with them, but you are not really into the same party scene that they are into.

Let them know how you feel. They have to know that you are not judging them or wanting to change them, you just want them to know that you are not really up for spending time with them at the bar, or out partying, etc. They can't change how they spend their time with you if you never tell them how you feel.

Ask them if they enjoy any other activities you could be part of. This is a simple way to try and spend time with your friends without having to deal with being in the party scene that you don't want to be part of.
A good idea is to plan activities that are free of the ingredients for partying. For example, you can have everyone over for a dinner party. You can get everyone out for a fun game of beach volleyball, or to get involved in a game night, or something that does not involve partying. You will be surprised how into it your friends might be, especially because if they party a lot, they may be getting as sick of it as you are.

If your friends just want to party, see what you can do to change it, or move on.