Just a heads up to those who don't do this interchange regularly The escalator from the eastbound overground platform to the Jubilee line is out of service, no idea for how long.
As a result the interchange there in the rush-hour is even more hideous than usual so do allow more time.
Or if you don't have to travel in peak times I'd advise you to wait.

Does it help to go up to the ticket office and down two flights?

Thats the only route you can use..
All passengers get routed that way by the station staff.