You need to be an Administrator to change the HomeGroup Password or to leave or
remove the HomeGroup.
How to Change the Windows 7 Homegroup Passwordhttp://www.sevenforums.com/tutorials/44002-homegroup-change-password.html
How to Disable “HomeGroup” Feature in Windows 7? (also to remove existing HomeGroups)http://www.askvg.com/how-to-disable-homegroup-feature-in-windows-7/
HomeGroup: frequently asked questions (also shows how to remove and delete homegroup)http://windows.microsoft.com/en-US/windows7/HomeGroup-frequently-asked-questions
Leave a homegrouphttp://windows.microsoft.com/en-US/windows7/Leave-a-homegroup