1
You can change the Windows UI font size by opening the settings app.
Go to Ease of Access - Display.
Then, use the Make text bigger slider to change the font size.
Please Note: this only changes the font size in modern UWP apps and most parts of the Windows interface.
2
There is no native method available in Windows to change the actual font used for the Windows user interface, that must be done by editing the registry and that is not advisable, because all the icons used in Windows interface are part of the Segoe font used in Windows and changing the user interface font will usually break the Windows icons.
This is the method, but I advise against doing this.
Open Notepad and paste the code below into a new document, then replace XXXX with the exact name of the font you want to use.
Then save that file with a .reg file extension, not a .txt file extension.
Then right click that file and select Merge, and confirm the merge, then restart your PC to apply the change.
.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Fonts]
"Segoe UI (TrueType)"=""
"Segoe UI Bold (TrueType)"=""
"Segoe UI Bold Italic (TrueType)"=""
"Segoe UI Italic (TrueType)"=""
"Segoe UI Light (TrueType)"=""
"Segoe UI Semibold (TrueType)"=""
"Segoe UI Symbol (TrueType)"=""
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\FontSubstitutes]
"Segoe UI"="XXXX"