How to adjust font sizes in Drupal 7.x

Hi folks.
I was wondering something.
Last night, when I had someone visit my website wich you all may review at:
http://keithnet.dyndns.org
I was told seriously that the font is not optimal for people with low vision.
As I have committed myself to insureing my site is optimized for low vision users as well as screen reader users, hear is what I need to know.
It should be noted that I'm using Druapl Core without modification, I.e. No eextra themes, etc.
What I'm using is the default Draupl core layout as designed after an installation witht he bartic theme.
Is there any way that I can adjust the font used through out the entire website?
According to my screen reader, it's all in font 8 and such.
What settings would be considered optimal?
Any ideas would help.
If you have useful vision, that would help as well. Please do let me know what you recommend I do.
If it involves heavy PHP code, I don't know enough code to do what must be done.
So i hope it is somewhere in the core interface and that a screenr eader only user mlike myself will be up to the task.
I cannot aford to pay a person anythign at all to help, so whatever you tel me to do I hope that what I am told is doable by a single person without any assistance, etc.
Thanks.