Upgrading Xpress 12 to 18 is as simple as installing Xpress 18 and copying your data to the c:\xpress18 folder. The first time you open up Xpress it will covert your version 12 company to version 18.
If you have Xpress 11, install version 18 and then open the conversion utility to convert from 11 to 12, then as above Xpress 18 will do the rest. Tee conversion utility is in the Sage Pastel folder.