By the way, I agree with KEW when he says:
I believe I read your response that you may not be able to alter the font sizes of the numbers along the axes in REW. But if you can transfer the raw data, such as SPL or impedance vs. frequency, in a spreadsheet format, you can make graphs in Excel where you have full control over the appearance of the graph. It takes some learning to get good at it, but the results are worth it.
There are other scientific graphing applications available that are easier to use, but you'd have to purchase them. Most people who have a PC or a Mac have Excel.