I Can't switch between AMD graphic card and intel HD in probook 4540s

hi i have a HP probook 4540s (cpu: core i5 3210m, graphic: amd 7650m, 2 gig, hard: 640 gig ). in windows 7 professional i installed only amd's graphic driver and the system could switch between amd graphic card and intel hd.
but in the gpu-z test software the frequency was 300 MHz and memory frequency was 180 MHz (the standard frequency for 7650 is 500 MHz ). then i install windows 8 pro to test the graphic card With the hope that its frequency will be 500. i install ONLY amd graphic card but the windows can't switch between amd and intel hd (i realized that from gpu-z , unigine heaven and resolution options of some games(intel hd only supports 1024*768 and 1366*768)).
so, my question: how can i switch between intel hd and amd graphic card in windows 8 (with the The theory frequncy (500 MHz))?