To change your point of sale system you will first need to create a new "Store".
In your Shogo account (app.shogo.io) Settings>Stores>New Store - select your new point of sale icon then follow the onscreen prompts for connection.
Once your new point of sale is set up Shogo can load the sales data prior to the creation of the new point of sale store.
When you have connected to your new point of sale Shogo can merge the the two stores (old point of sale and new). This will streamline your sales data into one store.