Adam Morley Stevens

Hi guys o/,at the mo i have the standard 17 inch subaru impreza wrx sportswagon alloys with 225 45 17 tyres fitted,what i would like to know is if i wanted to fit 18 inch alloys to my car what if anything would i need to do,also i would be intrested in buying 17 inch wrx bugeye alloys that have been painted gunmetal or anthracite including 18 inch if they will fit my car,had my scooby since christmas and just starting to learn about them now so sorry if i sound a bit lame,hope somebody on here will be kind enough to give me the info i need especially when it comes to 18 inch alloys,my wrx is standard and it,s a big learning curve for me.