New POS client. Help needed.

I have a client who has taken over a business using POS. I have hand minimal exposure to POS and need so me help please. Does anyone have any notes on how to manage the POS to change buttons and fix items listings and how to upload from Reckon Accounts to POS etc. It is a grocery shop. I need to ensure that the setup is the most simpliest but effective for this client. Any help would be much appreciated