How do I change fonts and adjust their size?
I downloaded a font and I want it to be used instead of the Ubuntu default font in files & folders names & the web browser, if there is a way to do so please tell me.
You need to install Gnome Tweak (it's in the Software Center). Once you install it, it will show up as "Advanced Settings" in apps in the Dash. Open it and choose "Fonts" from the menu on the left, and you'll see a page which allows you to change the fonts Ubuntu uses.