Thanks for posting your question on Justanswer.com, a global paid independent support site.My Name is ***** ***** I will be assisting you today. As I don't know, what you have tried so far and which font you want to change, I am giving you two methods below, please try them out. Let me know if you need any further help otherwise please remember to give a positive rating, as that is the only way I am compensated for my time and effort.
To change font size:
Select Edit < Preferences...< Register to the right you will see Register Appearance and in this box you will have the option for font size. Please note this will change the font size of the register itself but will not change the font size of the accounts list to the left of the register.
As it looks like this bug only happens with TruType fonts. Since most windows fonts are TruType, that can be a problem, but there are a few old-style windows fonts available that you can use for a workaround. The System font is a good choice. To use this workaround, do the following:
It might take a moment for the app to reset, but this should get rid of the monster font on Windows 8.1 problem.