Recently i had added a 2GB DDR3 ram in my acer laptop. As a result my total ram is 4GB (2x2). I was running ubuntu 12.04 32bit(pae kernel). Everything was working fine. Now i have upgraded (new install) to 13.04 64bit. Suddenly i noticed that system is showing only 1.7GB. So i run lshw to ensure the fact. But lshw shows correct result (4GB = 2x2). How could i solve this??? There is no settings in BIOS for ram at all. My system is newly installed. No additional applications is installed except amd-catalyst driver.

System:

Acer aspire 4250 E-450 apu

Note: BISO also showing that 4GB ram installed.