for all which are searching for a way to make buttons/text bigger or smaller on your display.
The plugin touchdisplay is using chromium to display the web-Interface. Chromium has the posibility to zoom the content.
Edit the file: /opt/volumiokiosk.sh and add the line --force-device-scale-factor=1.5
replace the 1.5 to your needs and restart service or pi
Enjoy the bigger or smaller UI