How can i fix or do i need to replace ?

Hi, i seem to have a leak coming form underneath the tank, i cannot se exactly where, but when pressure in the boiler builds some water comes out, only a little and is running down the side of the steel casing on to the wooden floor,
would i need a new tank? can i get this seperately? or can the tank if leaking be fixed/ sorry if this sounds stupid, havent got a clue about boilers regards