How do I change the current settings of the environment variables for ABAQUS?

Create a file called abaqus_v6.env in the directory from which ABAQUS is run which contains lines of environment variables you want to change set equal to new values. However make sure that the computer on which you are running ABAQUS can support the changes. For example you can increase the memory used by ABAQUS. But you cannot increase this beyond what is available in the computer. 
Example : Include the following lines in the abaqus_v6.env file to increase the size of pre_memory and the standard_memory used by ABAQUS. 
For earlier versions of ABAQUS :

pre_memory="400 mb"
standard_memory="500 mb"

If running ABAQUS on a PC then make these to the system copy which will be in the ABAQUS installation directory : 
C:\ABAQUS\6.8-1\site\abaqus_v6.env