Summarize the following:
If you're in a party and wanted to leave, simply type /leave in your chat window. You will be completely removed from the party list and will no longer be able to receive EXP from your party members. To join the party again after leaving, you need to ask the party leader to invite you again. Another way to leave the party is by clicking the “Leave Party” button found on the party window. To open the window, simply press Alt+Z and then choose the button at the bottom left to leave. There are times that members in the party went offline and didn't come back after an hour or so. Or, for whatever reason, you wanted to kick a member out from your party. To do this, open your party window and then right-click on the name from the list. Choose “Kick from Party” to remove them.

Summary:
Type Leave Command. Use Party Window. Remove Members.