Click on the relevant category in the left hand side menu or use the Sort option on top of the right had side and all the products in that category will be displyed on right hand side.
Click on the bin icon below the product thumbnail you want to delete. Pls. note that if a product is in two categories clicking on the bin icon will delete it from both the categories.
In case you want to delete the product from only one category pls. click on the product thumbnail>> Modify Product>> Under categories heading click on the cross next to the category dropdown>> Click save down the bottom.
The product will be deleted from all the categories it appears under.