Check out the Notes Help topic "Customizing Lotus Notes for Accessibility". Here is the relevant information for what you need:
The notes.ini file configuration file is located in your IBM Lotus Notes directory. It stores information about your personal Lotus Notes installation. If you need to use slightly larger or smaller fonts at all times, close Lotus Notes, open your notes.ini file, and add the following setting as a new line anywhere in the file:
Here, n is the number of points added to the default size and is a number between -1 and 25. For example, if you want to increase the font size by 3 points, you would type:
Caution Using a value of 4 or higher may result in formatting problems. If you need to use fonts that large, it is best to change your display fonts in Windows, which will affect all the programs on your computer, including Lotus Notes.
Notes 8 Standard (with Admin and Designer)
Dell GX280 3.2 GHz, HT, 1 GB RAM