Please Can Anyone Help Me The Question Might Already Have Been Asked.i Have Not Got A Clue About Alloys.

Will The New 11 Spoke 18 Inch Alloys Gm Ronal 7.5jx18h2et37 Which Are On The Astra H Twintop Fit My Astra G 2.0 Turbo Cabrio,on A 03 Plate
Would It Be A Straight Swap Or Would I Have To Modify And What Is The Best Size Tyre To Use Because I Have Not Got A Clue.
Please Can Anyone Help