Do you mean edit the URL or use an URL shortener?
For the first one, on the landing page in the Main Marketo UI, click the "Landing Page actions -> URL Tools -> Edit URL Settings" You will also be able to create URL redirects there.
For the second, nothing is built in Marketo. You will need to use an external shortner.
I really have to show you guys Bitlify!, my little Marketo UI helper to create Bitlinks within Marketo. One of these days...