remove old graphics card, and install new one in ubuntu14.04

The GeForce GT 610 graphics card can use either the NVIDIA proprietary driver or the Nouveau open source driver. If you are replacing an old Nvidia graphics card with a new Nvidia graphics card it should work with the existing graphics card driver, otherwise uninstall the existing graphics card driver before you put in the new graphics card, then after you boot with the new graphics card open the Additional Drivers utility (Dash -> Additional Drivers) and install the proprietary graphics driver from there.

In the below screenshot, you can see that the GeForce GT 610 graphics card is using the recommended driver, nvidia-331.