Hi Paulie,
You may uninstall Studio 9 to conserve space. However, if Studio 12 gives you error after this, run Studio 12 installer and do a repair.
On your second inquiry, you might be referring to this procedure.
However, Studio 12 is tested to transfer contents from Studio 10 and 11 only. If you purchased premium contents from Studio 9, you would need to use the Bonus DVD from Studio 11 which you can download from here.