What's the correct step to switch working copy to a specific branch?

[Lei Shi]

For example, my working copy is https://src.chromium.org/chrome/releases/24.0.1278.0, and I want to switch to https://src.chromium.org/chrome/releases/24.0.1279.0.

I'v tried just edit the name and url in .gclient file, but that will make whole working copy corrupt(.svn directory disappear).

Do I need a fresh check out whenever I want to switch working copy to a specific branch?