In the Human resources screen, you can't adjust the number of employees you have in the Admin screen. The game simply wont let you click on anything.
You can change pay rates though, just not number of employees.
Sounds like a transparent label overlapping the area where you have to click. Should be an easy fix, i'll get to it for 1.18.1
Ah, I was thinking branch and not admin. (Internally Branch expenses are shown as Admin expenses. Which confuses me sometimes.)
Admin, as in office workers is currently something that can't be adjusted. Eventually I may change this, specially now that we have action memos and in the future long term costs such as retirement plans/pensions/etc... But until that time I have set the scroll bar and text boxes as non-visible.