I suggest that you do it by department
Go to the Main Menu / Stock Systems / Supply Report
The first step is to check the Over Supply Report.
Put 100% in the box.
Select the option to show all
Select option Returns
Now click Show Report.
These are all the products you have received and never sold in the period chosen. I would suggest these are the first ones to cull.
Now if you need more room, select the Magazine Supply Report. Although the report was designed for magazines, it will work with any item.
Now I suggest you do this step by a supplier.
Now select a supplier here and period and then click Get Data.
Now on the reports, you will see a listing of the items sold by numbers. Note the bottom selling items.
Actually it is surprising how much can be culled with little effect on sales.
See how you go and let me know how it went.
The idea here being is to be very surgical in your approach rather than blunt.