I've got a repository where HEAD is a predecessor of master. HEAD is the version I want to keep. How can I set master back to the previous version HEAD?
checkout master and then reset the branch to the commit you want. Be careful: If you checkout master HEAD will point to master afterwards. You may loose your last reference to the commit you want to reset to. A safe method is: "create branch temp on current HEAD. checkout master. reset hard to temp. delete branch temp"
In the Git Repositories view you open the Branches folder, select the branch you want to delete and do right click -> Delete Branch.
If there are commits in that branch, which you don't have merged to another (i.e. which you would lose on branch delete) you get a warning message, which you have to confirm.
Branches can also be deleted from the 'Branches' dialog. You can get there from the 'Checkout branch, tag, or reference' toolbar item (looks like an inverted pitch-fork) or from the 'Team -> Switch To -> Other...' right-click menu item.
As noted in the previous response, the underlying operation is like
git branch -d
as opposed to
git branch -D
You have to confirm the deletion if the branch has un-merged commits.