I suggest that you consult the acer travelmate 5710 (5720) user manual. If you do not have a copy, then a copy can be downloaded from www.acer.com.au
The amount of memory assigned for use with your integrated display adapter is controlled through BIOS settings. In the case of the Travelmate 5720 it has 8 MB of dedicated memory for the video adapter. Up to 358 MB of shared system memory may be allocated for use with the display adapter.
To enter the BIOS, power the laptop up and press F2 while it is doing it's power on self test (POST).
Navigate through the BIOS utility options and you will find an entry for video memory. Select that amount of memory that you want to share with the video adapter. save the settings and exit the BIOS utility.