There are a couple of approaches. The easiest is to select all the boxes at the top level and then copy and paste into a new process. This works but can sometimes take a while for a large process.
Perhaps a better way is to use the XML export feature. Open the XML export window in your process and then copy all the text.
Now create a new process in the other workspace, open it and go to Edit Mode. Open the XML Export window in this new process, delete everything and then paste the XML from the previous process.
The one thing to watch out for is any images. These might not work and could need updating.