ram adding RAM OK trying the again sorry i am a newbie

Feb 17, 2018
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OK i have HP desk top PC with 3 GB ram 2-1 GB and 2- 512 taking out the 2-512's . how much ram can i use the pc is 10 years old.
the ram thats in there hynix 512 1Rx8 pc2-5300U-555-12 HYMP564U64CP8-Y5 AB 0721 This is my first time sorry in advance