For Custom Foods, My P.L.A.N. requires that, for whatever serving size you choose (cup, T, tsp, etc.) you also enter the weight of that amount of the product in grams. I get this number from the package label of whatever I'm entering as a Custom Food.

Once you've used a Custom Food as a Daily Entry, you cannot delete it. You can, however, edit it. Bring your Custom Food up on your screen, and click on the "Customize" button that you'll see on the left, right below the "Add to" button. All you have to do then is make whatever changes you like in your entry, then scroll all the way down to the bottom of the page and click the "Replace Custom Food" button.

If you have not used your Custom Food as a Daily Entry, just go to your Custom Foods list (to find that, scroll down and click on Food Lists in the menu on the left of the page. Click the Custom Foods link at the top of that page to get to the list.) Find your Custom Food on your list, click the box immediately to the left of it, go to the right hand side at the bottom of the page and choose Delete from the menu. Then click the word "Go." That should remove it for you.