I want to clone a GitHub repository from Visual Studio and the default path is C:\\Users\\[User]\\Sources\\Repos\\[NameOfProject]
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In Visual Studio 2015 / 2017 / 2019:
For VS2013 v4+ and VS2015
Click on "Settings" (from either the project Home menu or from the top dropdown menu), then select "Git Settings." You will see a Global Setting of "Default Repository Location" (the one you want). Change it and click Update.
In addition to the Team Explorer's Git settings...
...you'll likely want to change the default project location:
Tools | Options | Projects and Solutions | Locations