From the campaign's overview page, you can quickly change the campaign's format type by clicking Options > Settings, choosing the campaign format you'd like to change to, and then submitting your changes.

WARNING: This will affect how your campaign displays live. If you're changing a live campaign, we'd recommend disabling the campaign on your website first, performing the campaign format change and adjusting the contents of the campaign format's variants in the builder before going live again.

Also, if you change a popup campaign to a landing page campaign, the popup campaign will be disabled by default, until you activate the campaign on the campaign's launch page.