How to change WinMerge font size

Update August 2019: in newer versions of Windows 10, you can increase only the text size in the new 'Make text bigger' option:

Settings > Ease of Access > Vision > Display > Make text bigger

Settings > System > Display > Change the size of text, apps and other items

You can adjust the size there.

Or if you want to specifically choose what you want the text size to change for, go to Control Panel > Appearance and Personalisation > Display > Make text and other items larger or smaller.

Here you can change the font size of title bars, menus, message boxes, palette titles, icons or tooltips:

It's not fully clear if you want to change the font in your terminal (are you using xterm?) or in your vconsole before issuing startx command.

To change the font size in xterm:

xterm*faceSize: 23