Right-click on the branch from which you want to switch and select "Integrate" (if in 2011 you select "Merge / Integration"). Then in the window that appears, enter the target.
Please note that to create a branch in a new location, you must provide permission to submit. So
// depot1 / main / ... // depot 2 / sandbox / ...
If you send permissions to // depot 1, but not to // depot 2, you cannot separate from // depot 1 to // depot2, but you can deduce from // depot 1 / main / ... to // depot1 / sandbox / ... as long as you have permissions for all // depot1
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