If, on the other hand, you want to nuke them entirely, go to iTunes and choose your Apps library. Click an app to select it, then press the Delete key. Another dialogue will ask you if you want to keep the app or move to the trash. (You may indeed want to keep them; Ted Landau recently posted a tip discussing why that can be useful.) You can remove the apps from your iTunes library, but keep them in a folder on your Mac just in case.
It may help to view the apps in your iTunes library in a list. Click the List button, then click the Purchase Date header to sort by the date you purchased the apps. (The Purchase Date is either the date you downloaded an app or, if it has been updated, the date of its last update.) Look at the apps with the oldest purchase dates to decide if you still use them. (If you don't see the Purchase Date column, press Command-J and select Purchase Date from the View Options window.)
There's one other way you can delete apps from your iTunes library, and it's one I use often. I have hundreds of apps, many that I use regularly, but most that I only tried out. It takes too long to go through my Apps library and try and remember what each app does. So I wait until there are updates.
In iTunes' Apps > Updates window, you'll see a list of new versions of apps that you can download, when an app has been updated. When I see an app in the Update window that I don't use anymore, I delete it. To do this, right-click on an app's icon and choose Delete. This deletes the app itself from your iTunes library, and also removes the update notification. The next time you sync your iOS devices, the apps you have deleted from your iTunes library will be removed from your devices.
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