hmoon :
I want to upgrade it and would like to know what graphics card is best for it. Also wondering if I need to replace some parts before buying a graphics card. Thanks.
The overall specs look great if you want to add a GPU. One thing though, the Powesupply is only 220 Watts which is very VERY low if you want to add a GPU.
For a new power supply that has an available 6-Pin connector for the GPU this is it ( Link Below)
http://www.ebay.com/itm/400W-for-HP-Pavilion-Slimline-S5000-Series-TFX0220D5WA-TFX0250D5W-Power-Supply-/33105242367
with that you can buy a GPU that uses around 250 Watts at max.
Id recommend the GTX 960 (you'd need to buy an adapter [2x Molex {$4}] to go with the card though or some other card with a max wattage of 250
You dont need to replace any parts except for the PSU.
Hope i helped
😀