I would like to know if it is possible to upgrade my graphics card? I am trying to use graphic intensive programs...

Question

Chipset Model:
NVIDIA GeForce 9400
  Type:
Display
  Bus:
PCI
  VRAM (Total):
256 MB
  Vendor:
NVIDIA (0x10de)
  Device ID:
0x0867
  Revision ID:
0x00b1
  ROM Revision:
3379
  Displays:
iMac:
  Resolution:
1920 x 1200
  Depth:
32-Bit Color
  Core Image:
Hardware Accelerated
  Main Display:
Yes
  Mirror:
Off
  Online:
Yes
  Quartz Extreme:
Supported
  Built-In:
Yes
VGA Display:
  Resolution:
1024 x 768 @ 60 Hz
  Depth:
32-Bit Color
  Core Image:
Hardware Accelerated
  Mirror:
Off
  Online:
Yes
  Quartz Extreme:
Supported
  Rotation:
Supported
  Adapter Type:
Mini DisplayPort To VGA Adapter
  Adapter Firmware Version:
1.03

Answer 1

What exactly what kind of graphics are you working with?
What applications are you using.
Are you working with video style graphics or still images and graphics?
If video are you working with 720p or 1080p video?
256 MBs of VRAM should be fine for doing regular still design type  graphics.
If you ard having issues, please tell us what they are.
It you have an older iMac, it maybe your CPU could be causing some issues.
It could be you are not using enough RAM memory to run the graphics applications you are using.
How full is your hard drive?
If your hard drive is getting full, this maybe causing your iMac to slow down.
Your issues maybe more than just GPU related.
What is the year, screen size, CPU speed and the amount of RAM installed into your iMac?