Ok, I will take a shot at this for you…
First of all, since you did not mention your version, I am going to assume you are using v11.
Secondly, you must download a template from the data import/export tool that includes your current data populated in the spreadsheet.
Now, the rest of what I tell you will reference the below screenshot of one of my v11 “Item Price” downloaded templates:
We are only interested in columns B, C, D, and E
In column B you will find a cryptic looking string in quotes.
If you are going to UPDATE records, then this column must be pre-populated in the template when you download it!!! If you download a blank template then column B is empty and all records you put in the template will in fact be used to create NEW Items in your price lists. The ONLY way to UPDATE a record is if you have the strings populated in column B first and they can only come from the database when you download a template ‘with data’
You can see in the example screenshot above that column B is already populated (as well as the others).
So, now all you nave to do is replace the values in column E with your new prices and save the spreadsheet. This new saved spreadsheet will be what you upload to the Import tool in order to change your prices.
A word of caution…
Break your price list up into groups of one thousand or less in order to keep the buffers from being over-run during the import process. If you know that your ERPNext server is running on less than 4gb of memory, then you might want to cut that number in half again just to speed up the process and reduce errors.
Hope this helps you out. These are my solutions and… Your mileage may vary