This is not a question about changing the font size in graphs produced using RStudio. I already know how to do that.
I use RStudio under Linux on a MacBook Pro with a 'retina' display. I use KDE as my window manager. I can (and do) enlarge the default font size in the user interface of other programs in KDE. I increase the font size for the user interface in Firefox and Thunderbird using program specific tools.
How do I increase the font size in the user interface - not the console, which is easy [Options -> Appearance -> font size], but, for example, the help text, the keyboard shortcuts list, and so on. At the moment I find these very hard to read. I've fiddled with everything I can fiddle with, but had no joy.
All help gratefully appreciated!
As some people pointed out, by clicking the ctrl & + together, you can enlarge the font size for everything including for the console & code script. (You will have to do it with a help page pop up as suggested by user3619015.) Then go to the global option and resize the fonts. That changes the font size for everything except the help page. So you will have larger fonts for the help page but everything else in your normal preferred font size.
Rstudio doesn't support changing fonts yet, at least for Linux server. However, one can change fonts in browser for a specific page. At least in chrome, you can customize fonts using an extension called font changer. I think it is packed with all GNU free fonts for legal issues. But, since you have the font files in the OS, like consolas, you can practically change to whatever font and size you like. Just play with it.
On a Mac you can do it by going to: view -> actual size or just with the key combo: cmd+= (not cmd++) to zoom in (bigger), cmd+- or zoom out or cmd+0 (zero) to go back to the actual size.
Help, Files, Packages can be opened in a new browser window where zoom in and out options are possible. Even a selected specific package can be opened in a new window for clear view
I had the same problem here using a MacBook Pro although not with KDE, but you could try on the menu of RStudio:
View -> Actual size
After a couple of days struggling to read the help, this worked: increased the size of letters in all windows of RStudio.
Here's how I got around the problem:
Simply copy and paste into your word processor or text editor. Text will be pasted in the default text.
I'm using Windows 8.1, Office 2013 and R 64 bit. Not optimal but it works.