Employee salaries can be updated under Employee Management > Employee Pay > Salary.
As a rule of thumb, click "Add New" when making changes - this will add a line on this screen and allow you to keep track of all past salary changes.
If you are making a salary change that should be effective immediately, choose Record Type: "Current Change". Once you've entered the new rate information, click Save.
If you wish to schedule an update in advance, choose Record Type: "Future Change". Keep in mind that date of the change refers to the pay period rather than check date. The employee's pay will change on the first payroll with a period end date later than the salary effective date.