RAM update

Comrades! Advise what to insert? Asus M5A97 motherboard (2 PCI, 2 PCI-E x1, 2 PCI-E x16, 4 DDR3 DIMM, Audio, Gigabit LAN) now installed 2 DIMM DDR3 4GB 533-1066 MHz lines 7 years ago, installed, did not change.