You should definitely upgrade your motherboard if you want to upgrade to an Intel Core i5-3XXX/4XXX, B75, H77, Z75 or Z77 for Intel Core i5-3XXX (Z75 and Z77 is for K CPU's) or H81, H87 Z87 and Intel Core i5-4XXX (Z87 is for K CPU's).
Most of the stuttering will be gone in CPU demanding games, FPS increase should be about 10FPS, unless you're going to get the K version of i5 and overclock it on a Z77/Z87 motherboard, what's your current motherboard?
My motherboard is FUJITSU D2990-A1 it came when i bought the computer, i dont really know much about motherboards but im assuming i need better one. Do you have any suggestions what i should get? Nothing too expensive.
You should definitely upgrade your motherboard if you want to upgrade to an Intel Core i5-3XXX/4XXX, B75, H77, Z75 or Z77 for Intel Core i5-3XXX (Z75 and Z77 is for K CPU's) or H81, H87 Z87 and Intel Core i5-4XXX (Z87 is for K CPU's).