If you do not wish to save your customer number you should skip the "Settings" option and go directly to the "Update" option. A window will appear where you should enter your customer number. It also allows you the option to save it or continue without saving your customer number. Note that it is more convenient for you to save the customer number for future reference since you will not have to enter it every time you update.
If you skip the "Settings" tab and go straight to "Update", this is the window you will get.