Change the text size on site globally!

Hi All, 

On my site the text is soooo tiny and it must be really off putting for new members and also doesn't allow the content to stand out. 

I willing to pay a fair price for someone to update this issue as I have already checked the forums for answers and couldn't not find a decent guide to follow to do this myself. 

I would like to have this done asap.

Many Thanks