There are 3 solutions for this requirement:
Solution 1:
- Go to Transactions > Purchases/Vendors > Pay Bills > List
 - Edit the Bill Payment for which check number needs to be changed
 - Change the Check Number and save
 
Solution 2:
- Go to Lists > Relationships > Vendors
 - View the Vendor record and go to Financial Tab > Transactions subtab.
 - Edit the Bill Payment, change the Check Number and Save
 
Solution 3:
- Go to Lists > Accounting > Accounts
 - View the Bank Account Register
 - Under Print column, put a checkmark on the Bill Payment that needs to be reprinted
 - Go to Transactions > Management > Print Checks and Forms > Checks
 - Choose a Bank account and put a checkmark on the Bill Payment to be printed
 - Change First Check Number to desired check number and click on Print