If you want to edit your contacts on your iPad, in the Contacts app, to delete a contact, open it and tap "Edit":
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Then scroll down and select this:
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To add a contact, tap the + here:
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And enter the information at the right.
It's easier editing a Gmail account if you have a smartphone. I prefer editing my contacts on my SGS 3, because it's easier done there. It would also be possible to edit them using a browser, in desktop view in your Gmail account. You could use the iPad for this.