In iTunes, go to the left column. At the top is the "Library" list. In that list should be a line for "Apps." Clicking on that will bring up all the apps installed on that iTunes account.
Browse to the app you want to delete, right click on it and select "Delete." iTunes will ask if you're certain, and, if you are - just delete it (I send my to the Recycle bin straight away ... figure if I took all the trouble to delete the app, why not?).
Hope that helps.
Marilyn