I'm not sure how to set your font so that the size stays the size you want, because I think it's different for each computer, but you can increase it by pressing the Ctrl and plus (+) together. To make it smaller just reverse it by pressing Ctrl and minus (-) instead of the plus (+) sign.

I hope that works... it does for me.

Otherwise, go to your help page and type in "adjust font size". You should get the directions on how to set it.