How can I delete/insert the iframe codes?

Thank you unfortunately it will not let me delete the current code or insert the new code: How do I do that.

When getting the iFrame Embed codes, you won't be editing it from the FORM BUILDER. You only need to copy it. If you wish to further customize/edit the codes, you can do that before you paste them on your website's source code.

In case we misunderstood your question, just get back to us with a bit more info and a clearer description of what you're trying to do so we can better assist you.