Software re-use

I bought a dell 4 years ago and it came with office. Can i load that onto my new system?

Generally if you remove it from the old system you can install it on another system. However some companies which preinstall software sometimes lock the software to their system or they don't provide a way of reinstalling.

I personally would make sure the software installs and works before removing it from the old system. It's common sense, but may be against the EULA.

Generally you can copy the third party software and install it on another machine. In practice it usually installs and runs. You will have to check your EULA on your individual copy installed on your Dell to see if it is legal.