Once you have been upgraded from one version to another, you cannot downgrade it. As one user commented, you can start over with a different username/password, but an easier solution is to create a new return under the same account. To do so, simply select Tools > Return manager, and create a new return. That way if you have carryforward data from a previous year, you can still bring it forward.
As for the initial question, if you select something in your tax profile (generally investment related in this instance) that needs to be done in premier, it will prompt you for the upgrade. If you made a mistake, you can cancel, go back and change your answers and the prompt should not re-appear.
As for the charge for your wife- it will still be charged at the Standard rate even if you upgrade to a different version, so for instance if you prepared a coupled return in standard, you would be charged 17.99 +17.99 (two Standards). If you were upgraded to premier, your charges would be 34.99 +17.99 (1 Premier plus 1 Standard)
