You are going to be severely limited when it comes to upgrading that platform.
You are better off building off of a newer motherboard.
To know for sure, you need to find out what model the motherboard is, then look it up on ASUS website to determine the hardware compatability.
Also, that case would not be good for decent gaming GPUs. Those things don't circulate air well. And they have tiny power supplies.
I would look at building a whole new setup, including case and power supply. I had an Essentio and I know the power supply they put in it just barely covered the supplied components.