There are different types of hot water dispensers. They come in various models, sizes and designs, of which you can find the best on the market here https://productspy.co.uk/best-hot-water-dispenser-reviews/
Due to the variety of sizes it is very important to check the user guide before you attempt to clean your model of dispenser.
In case you cannot find the user guide that came with your product, you can check online to get the appropriate one for your model. All you have to do is check based on the brand and model number.
Before you start the cleaning process, you need to unplug the device from the power unit and start cleaning from the outside.
Before you start cleaning, unplug the dispenser from the power unit and allow it to cool down. Do not clean the device while it is still hot to avoid getting scalded.