This blog shows on how to do a GAC UnInstallation at Runtime

Public Sub GacRemove(ByVal AssemblyPath As String)
Dim instance2 As System.EnterpriseServices.Internal.Publish
instance2 = New System.EnterpriseServices.Internal.Publish
instance2.GacRemove(AssemblyPath)
End Sub

strQuerystring = "Specify full path of dll"
GacInstall(strQuerystring)