Update
I may have solved this problem:
I changed all these default tiny unreadable fonts from something (tahoma?) to Verdana! That did it!!
The very nice font resulting from the solution below compared to the default tiny font size appears now twice bigger and much more readable in all relevant - previously unreachable - places of Construct 2 mentioned by users here in this topic.
It is not possible to change the font size. However you may change the font type.
To do this:
1. Open the Start Menu
2. In the Start Menu Search box type regedit and press Enter.
3. Locate: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\FontSubstitutes
4. In the right pane, right click on MS Shell Dlg and click on Modify.
5. Type in the name of the font you want to use and click on OK
NOTE: You can get the name of the font from the Font Folder Location C:\Windows\Fonts. Right click on the single font and click on Properties to see the file name. For a font group, you will need to open it first to see the single fonts in it. Be sure that you use the exact same font name that is listed. Do not include the Regular part or file extension in the font name. For example, I would type Impact instead of Impact Regular or Impact.ttf.
6. In the right pane, right click on MS Shell Dlg 2 and click on Modify
7. Type in the name of the font you want to use and click on OK
8. Close regedit.
9. Logoff and logon, or restart the computer to apply the font changes.
Disclaimer:
To do so: Important this section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 (http://support.microsoft.com/kb/322756/ )
How to back up and restore the registry in Windows
For Win 7:
askvg.com/how-to-access-advanced-appearance-settings-option-to-change-text-size-in-windows-8