How to access memory with Custom IP?

Hello,

I have a working example which reads image data from host PC transfer it to an FPGA using PCIe which store in memory then a frame reader is used to show the image on a vga screen.

I have developed a custom entity which has to make calculations to the data stored in memory. The question is, as i am beginner here, how can I access the image data in the memory so I can make the calculation then I can re-save the data in the memory before it is shown again on the VGA screen.

The developing board is de2i-150.

Thank you in advanced,

Albar