From the Windows, Start, go to Printers and Scanners.
Go to Print Server Properties (Note: you may not have access to this. If not, you will have to get a System Administrator to do this for you).
Click Create a new form.
The form name field should now be editable. You can call the new form whatever you wish, but payslips seems like the most logical choice.
You will have to measure the length of the actual payslip (metric or English) and enter the value in the left most height field.
(Note: do not worry about margins for now).
Click Save Form and Close.
In Printers and Scanners, if the payslip printer is shown (Note: and it is only being used to print payslips), Click on the printer, Click Manage and select Printing Preferences.
There should be a paper size option and a drop-down selection window associated with it. Click the drop-down menu and select payslips (Note: or whatever you named the new form) from the list. Click OK to all screens.
Note: The above may vary slightly depending on the version of Windows you are on, and the make/model of printer, but idea is the same.)