Found under "Tools".
Click on the arrow next to data like below and select "Import".
Click 'next' on the initial pop up screen.
Select the type of data you want to import, in this example I am using 'Products' but this could be Groups, Major Groups, Suppliers etc.
The import format will stay the same at 'Text File' as we are wanting it to pick up a CSV file format.
If you do use a CSV file format then it must have the data inside formatted with headers for the importer to pick up, the product code must be a "number" format and any currency columns must be to 2 decimal places.
Select the file you want to import.
The update method is important for your desired outcome, if you want it just to add new products then select 'Only Add New', otherwise the 'Add New and Update Existing' will change existing products it finds on the same product code as well as adding new ones.
Selecting 'During import strip out any characters which may cause issues' will remove anything in the csv file which could cause a product to not import correctly to be removed, this could be a '&' in the price column for example.
The 'Lookup Product by' is how the importer searches for the product in your chosen file format.
The next screen is below.
The file format I have chosen is CSV, however you can change this to your file format. CSV is recommended.
The first line ideally needs to contain the headers for your columns, so that the importer can match the columns in your CSV to the table columns in SQL.
As you can see below, the screen now finds the columns as mentioned above and matches these. If it doesn't match then it is shown here on one line in the header, this then allows you to match it yourself by clicking and dragging the field criteria across to the appropriate column.
Click 'next' and then 'finish'.
This will begin importing your file into the product list. This would be the same for whatever you chose to import into (Groups, Major groups).
The results of this should look like follows, if it finds a product to update on the same product code then it will update that too.