If you’re in a position to do so, you can cancel your credit card instead.
As far as unsecured credit goes (credit not backed by an asset like real estate), your credit card should match your asset position including your income level.
If you have a high credit limit compared to your asset position, this is generally frowned upon by the banks.
Cancelling your credit card can be a good step to borrowing the amount you need so simply call your credit provider and ask them to do so.
Also, ask for a letter as evidence to provide your bank when applying for your mortgage.
Before you close the card, don’t forget to use up any points you have!
You can transfer them to a frequent flyer program or spend them.