how to bleed up diesel after changing the filters?

Fuel system is designed to be self -bleeding - at least that's what the Ford Workshop manual would have you believe.
You haven't said which model Cargo it is - so there are a few engine types with differing fuel systems.

But typical scenarios would be:
If its a Ford 110 engine with a Bosch injector pump, there are bleed screws (need a BIG screwdriver - say 10 x 200) on the side of the injector pump - slacken these in turn until there is only bubble free diesel coming out of them. There are 2 bleed screws (with hexagon heads - 13 mm A/F probably) on top of the fuel filter housing - one over each filter.
Depending on how you went about changing the fuel filters, there could be air in the supply pipe from the filters to the injector pump - this pipe rises like a syphon. Might have to slacken union at injector pump end to clear air while operating primer/lift pump by hand.

Make sure that the rubber seal/washer between the top of the glass bowl and the pre-filter/water separator housing is in place (can easily be dislodged). If this is missing, all you will get is continuous ingress of air and frothy diesel will continue to appear at bleed screws and no amount of bleeding will make any difference. A simple thing but enough to prevent the engine from starting!

JD
November 2008