you have to buy more memory at a computer store like best buy or microcenter. and they are small chips that you put in yourself. the store needs to know what kind of computer you have. I would call them first and ask questions like price . you usually take old memory out and replace it with other chips.
By memory I assume you mean RAM in which case you need to upgrade. Buy on newegg or something but make sure to read reviews and buy the right kind of ram whether is DDR2 or DDR3 and speeds your PC can handle and laptop or desktop.