If your pay run dates need to change for pays going forward, simply go into Company >> Pay Dates and click Edit. This will let you select the Pay Period End Date of the appropriate pay schedule (weekly, fortnightly, monthly) and the pay runs will adjust dates accordingly.
Pay Period Start Dates cannot be edited and are a result of the previous pay period's end date.
If you have made mistakes with past, completed pay run dates then our support staff may be able to assist.