By default FlatRedBall templates build the debug configuration. These templates are distributed with release and debug versions of the libraries being used in the project. Therefore, to switch between release and debug you should also switch which set of libraries you are referencing. The steps to switch between debug and release depend on whether the application is linking to prebuilt binaries or source.
To switch a DesktopGL template to release:
Open your project in Visual Studio
Change the configuration from Debug to Relese
Expand your project in the Solution Explorer, and expand the References item
Right-click on one of the FlatRedBall projects and select Properties
In the Properties window, find the location where the FlatRedBall library is located
Once the properties window is open, identify all of the libraries which are being being referenced out of your game's Libraries folder.
In the case of DesktopGL these are:
FlatRedBall.Forms
FlatRedBallDesktopGL
GumCoreXnaPc
StateInterpolation
Remove these references from your project by right clicking and selecting Remove
After you removed the references, right-click on your project and select Add Reference...
Click the Browse... button
Navigate to your project's folder. Select the Libraries/DesktopGL/Release folder
Add the libraries which were removed in the previous step from the Release folder
Click OK
If you are going to build your game in Debug mode, you should link Debug FlatRedBall .dlls. Similarly, if you are going to build your game in Release, you should link Release FlatRedBall .dlls. Mixing Debug and Release may result in compile errors, as FlatRedBall provides additional classes and members in Debug mode which code generation relies upon for improved diagnostics.
If your project links to FlatRedBall Source, then you only need to switch the configuration of your project:
All libraries should switch to release automatically.