if that doesn't work, which it might, try reformatting your computer. That should help with the memory problems. For the lag, simply turn most of the settings to off or low. My comp has the minimal video card and memory specs and it runs perfectly smooth w/ all the settings at off or low.
NO NO NO ! Arrf , do not reformat your computer !
I'm an I.T technicians assistant , do NOT under any circumstances re-format unless you know what you're doing - I have seen so many people coming in to the shop with "Dead" pc's . They don't know how to sort out windows etc etc . . . . . . .
Please provide me with your pc's specs - Then I may be able to help you . . . .
Re-formatting a pc's hard drive is a lot more complicated than re-formatting a pen drive.
So , your pc's specs please , and then I'll reply back with some solutions.