In the context of your code, do you already know where the folder is? I don't believe that any of the Pro/TOOLKIT APIs have a specific "delete from folder" type function... but you could always use the windows APIs for this?
You would include your windows headers/libs. Then, collect files in the desired directory using "FindFirstFile" (usually "FindFirstFileW"). Alternatively, you could also collect files in the directory using the Pro/Toolkit function "ProFilesList".
From there, you could call "DeleteFile", (usually "DeleteFileW") on anything with a PRT, ASM, or DRW extension. or There's also obviously functionality inside of the c++ std lib too - http://www.cplusplus.com/reference/cstdio/remove/
So it really just depends on how "compliant" you are trying to be with C++ standards vs how much you want to leverage OS-specific methods:
Past that, if you are instead trying to "get" the directory of a model that is already loaded into Creo... you could get the path of the mode. If you are using Pro/TOOLKIT, I believe you can do that with "ProModel" (as opposed to ProMdl). If you are using Object Toolkit (OTK), you can do this with the pfcModelDescriptor.
Hope this helps.