Joe wrote:
I currently have an Oystercard, which I used for Prepay a few weeks
back. It currently has no Travelcards or money on it. If I take it to
the tube station, will they put a Oneday Travelcard on it, or will they
only put more Prepay (or 7day Travelcard) on it?


More prepay - yes

7 Day travelcard yes.

1 Day travelcard - not possible, but if you use prepay it will cap at
the price of a one day travelcard (for most journeys).

Tim