Signed up while running SETI, but have now dropped SETI on this machine as am going to run it on a smaller otherwise not used machine. How do I change preferences to reflect only running the one so that it gets the full share?

kaj_aussie

Have you 'detached' from SETI (right click on SETI in the projects tab of BOINC)? If so, then BOINC will know that it is only running one project on that machine and will give the full share. The share you assign in preferences won't matter.