Add and Remove a assembly from GAC

To install assembly in Cache use  Gacutil.
Goto "Visual Studio Command Prompt" and type "gacutil -i <assembly_name>", where (assembly_name) is the DLL name of the project.
To uninstall assembly, type gacutil –u <assembly name> in  Visual Studio Command Prompt.

Global Assembly Cache

While using shared assemblies, to avoid Assembly being overwritten by a different version of the same assembly , shared assemblies are placed in a special directory subtree in the file system, known as the global assembly cache (GAC).
Placing shared assemblies can be done by special .Net Utilities Only.