The only advice I can give there is, wait until your insurance is up for renewal and then phone around different companies for quotes and state the new wheels (

if you've only just took the policy out, some companies aren't as fussy as others

), changing mid policy will also incur costs.
Other readers, it's worth a quick call to your insurance company before you purchase a mod to check on the extra cost, what you thought was a good deal on a set of wheels etc... etc... could not be such a good deal when the insurance add their whack ££££££ on top, ultimately leaving you under or not insured (if you fit the mod), or left with something you can't fit because it will invalidate your insurance or cost you loads to upgrade your insurance

.