I just bought a laptop with the AMD A8-5745M. It's great and plays the games I need it to, except for some more intense ones (Payday 2 and Saints Row the Third mostly). Anyway, I know that the APU uses on-board memory, but I can't seem to find a way to allocate more than what it's using (it's using less than a gig). I looked through the Drivers, and couldn't find anything, and I also wasn't sure of how I'd word in when googling. The laptop has 6 gigs, and I wouldn't mind loosing some of that at all.
It's pointless allocating more ram to the iGPU if it doesn't have the "horsepower" to utilize it. If you're wanting more power, you'll need to buy something else.
That APU is fine with 2GB of DDR3. The problem is laptop manufacturers are morons and lock out the option to give more RAM to the APU GPU and force you to run slow 1600 MHz or 1333 MHz RAM.
I am not familiar with APU-s but usually the settings to change the available memory for the iGPU is in the BIOS. But since it is a laptop that option could be locked out.
I would also say that having more VRAM doesn't necessarily give higher FPS unless the game is actually need more. But with more VRAM you could also use higher textures with minimal performance impact.
It would be in the Northbridge section of the bios. if its not locked anyway. by default it should be on "auto" mode which only allocates what is needed to the iGPU. so lets say im playing AOE 2 and i need 500mb of VRAM (just an example, not real numbers) it will take that 500mb from the system RAM and use it. If your playing Minecraft w/ shaders and other mods and need 2GB of vRAM it will allocate it itself. just some examples. My ASRock motherboard has the function to auto select ram needs, but im assuming that all motherboards do, so you shouldnt ever need to change it really. Just note that you cannot go over 2GB of vRAM and that the APU is severely limited to the speed of the RAM. 1333mhz is just not gonna cut it and 1600mhz is very sub-optimal for an APU. 1866mhz i find is the best value for performance, but most laptop carriers only support 1333 or 1600 unless it is a gaming/workstation notebook.