To customize the Payslip format, please make sure that you have Report Designer module included in your license package.

Go to License

Click on the product key

At Modules > Make sure the Report Designer is ticked.

Go to Report Files > Filter report type to Payslip> At the Payslip format you want to amend, Click on Design

Select the cell you want to change font. (You may Ctrl+click to select multiple cells)

At the left side under Properties. scroll until you find Appearance > Expand Appearance> Expand Font. You can manage your font here.