Maybe someone from support can give a more detailed answer but if I where going to do this, here's what I'd do. Don't follow this advice if you're using Service Desk. In that case you should contact support.

1. Check to make sure that you are using SQL persistence for workflows 
2. Turn of Timeouts and Escalations on this existing server and then turn off Workflow Service and IIS
3. Backup the database and restore it to the new database server. Take the old DB offline to ensure nothing is connecting to it while testing the new server.
4. Install Workflow on the new server and choose the existing database that points to the new database server. Leave the Background Processing roll unchecked during install!
5. Deploy all projects to the new server and configure app pools if necessary. 
6. Copy custom libs from old server to new. They can be found in install directory/shared/customlib
7. Check Workflow Explorer on both servers and ensure the new server has exact credentials as the old server.
8. Were you using machine name or DNS entry to reach the old server? DNS: just change that to point to the new server. Machine name is more complicated as you'll need to change database records. Alternatively, if you can rename the old server then give the new server the existing name it would save you headache.
9. Test the workflows a bit to make sure everything looks good before enabling timeouts and escalations.
10. Enable timeouts and escalations.

I think that should do it. Remember to back up everything first.