Difficult to say. The motherboard details mentions brand but not model.
The processor is ok - but I can't say if you could upgrade higher because I can't find out the tdp.
You will be able to upgrade your gpu no problem - but will have to upgrade your psu as well - and judging by the size you won't get a full-length card in the case comfortably, but that only matters if you want a double slot card. Low profile would be the way to go I think. So maybe upto a 6770.
You should be able to upgrade to 8GB of ram easily enough.
In essence you can make this into a respectable system - but I wouldn't expect miracles.
I have tried to find out more about this system but it is from a small vendor, and have been unable to find anything solid on it.
Contact them (shinobee Gaming). See if they have the same PC with better video. The card in there (Radeon HD 5450) costs them $25US and will not game. A $100US card will game nicely (say the 6670 suggested). Use this article for ref http://www.tomshardware.com/reviews/gaming-performance-... especially the hierarchy table on the last page. Note the size of your monitor (1920x1080 or 1024X768 or whatever) makes a huge difference in how strong a video card you need to have to have something playable.
If you cannot contact them (shinobee Gaming) then think thru how you are going to get your PC serviced if it breaks or plan on doing that yourself.