Updating a Marketo Landing Page URL is pretty easy. Follow the steps below to edit URL settings.
Step 1: Right-click on the landing page you would like to update. Select URL Tools and Edit URL Settings.
Step 2: Enter the new URL in the red box indicated below.
Step 3: If you have cloned a full program and just need to clean-up the URL or the existing URL has never been referenced, choose “Throw away” and click Save. If you're changing the URL for a page that is already live, proceed to Step 4.
Step 4: If you need to update the URL of an existing landing page that has been used for communications or is referenced elsewhere, choose “Keep both URLs” and click Save. Marketo will automatically set-up a redirect rule.
Source: Marketo Community