I need to alter the pay dates to the last Friday in the month. I can't see an option to do that. Does anybody have the answer please?

Hello, Lintama.

Are you using QuickBooks Online Payroll? If so, setting up your payroll schedule to every last Friday of the month is unavailable. For now, you can only select a specific date of the month (for instance every 5th of the month). 

For additional information about editing payroll schedule, please check this article: https://quickbooks.intuit.com/learn-support/en-us/help-articles/edit-your-company-pay-schedule-in-quickbooks-online-standard/00/242891

Also, you might want to try using PaySuite for more payroll schedule options.

 
Stay around if you require further assistance.