Although not supported, it is possible. The method varies slightly with cameras and video servers. This is considered advanced and should not be attempted by anyone not accustomed to manually editing files/scripts. Please ensure that you have the latest firmware before making any changes.
NetCam:
Log in to your camera here:
And click on "Manual Config". In the list of files, look for ftp0.scr and click on "Edit". Copy the existing lines and paste under "quit".
Edit it for the new server and click on "Save". When done saving, click on "Save configuration files". To test the script, you can telnet to your camera's IP address and run:
This will run the script real time where you can monitor for errors.
WARNING - If you make any changes in the FTP section in the camera's configuration you will overwrite your custom file.
Video Server:
Same method as above except that each camera has it's own FTP file and each will need to be edited.