How do I increase the size of the menu bar on my imac?

Just got a new imac and the menu bar is so small, I can barely read it. How can I increase the size of the menu bar for easier reading? We have made the icons at the bottom of the page large, but the menu bar on top is tiny. Sigh. Also, what is the best way to retrieve a new password for a guest account?

Thanks for your help.