You can apply a pay increase to all employees at once.
Go to the Employers Default Pay Options: click on the employer name in the main menu and choose 'Edit Details' then switch to the Pay Options tab.
Click the button labeled "Apply a Pay Increase To All Employees".
Enter the amount by which you want to increase pay and click the "Apply to All Employees" button.
The default pay options for all existing employees will immediately be updated accordingly.