End user clients cannot use the Accountants Edition.  That is only for accountants and consultants to help support clients who may use any of the four regular data entry versions.

If they wish to move from Quantum to Premium, it may be possible but would require the services of Tony Martin at Code 6 Programming to modify the file.  He cannot always do it if there is a lot of the Quantum features used.  So it is best to contact him for advice on that.  He would attempt to keep all historical information in the file.

I am not a Sage employee, I am a consultant so you may wish to wait for someone else to confirm this.