shuld i buy 2x used 4gb ddr3 1333mhz ram  or 1x new 4gb ddr3 ram tho?

currently tis lappy used 2x 2gb ram which is kinda sux.. i buy new ram then i will get 6gb ram and 1x 2gb ram not use.. if buy used one i can get 8gb ram and 2x2gb ram not use

how much ssd cost?
if change hdd then the current hdd can be used as external rite?

Hi there. Here's my problem. OVERHEATING. I am sick of it.. I own an acer aspire 5750g(gt630m,8gb ram,i5 2450m). I've already opened it up, cooled the vents and the cooler, repasted the gpu and cpu, reinstalled windows. I realised my pc is sometimes at 80-85C on idle and i noticed that my fan was not working. It's not working all the time.
P.s: i updated the bios from 1.15 to 1.21 yesterday, i see no improvements.
Any help would be much appreciated.