Here is a summary to do the same task after you have maybe upgraded the emonpi:
cd /opt/openenergymonitor/emonpi/firmware/src
sudo nano src.ino >> EDIT TIME_BETWEEN_READINGS= 5000;
cd ..
sudo systemctl stop emonhub
sudo platformio run -t upload
sudo systemctl start emonhub
Edit - formatted text. Moderator, BT