how do you change a payment from check pay to quick pay

Quick Pay can only be used if the biller's name can be found in the list of supported billers. From the Bills, Income & Transfers combined view select "+"(Add Reminder icon), Online Bill and search for the biller name.

If the biller is not available, I recommend you logon directly to the biller's website and authorize them to direct debit (aka PAC Draft, Autopay, APS, etc.) the next and all future payments from your checking account or a credit card. The biller's computer system will do all the work for you to make an electronic debit on the due date and you don't have to worry about being late.

In Quicken unlink the bill and just record a scheduled reminder which does not execute as an online payment into your account register on or before the Due Date and before you download transactions from the bank or credit card containing the payment transaction. That will allow Quicken to match your register transaction to the downloaded data and not cause any further issues.

If all else fails, write (and print) a paper check from Quicken and mail it yourself. About 10 days' lead-time should suffice for mailing and for processing by the biller.