How do I get the most out, I don't want any s**t left in the engine. I bought a bottle of flush, but is there anything else to get the most crap out of the engine with the oil.

Also I have 4.5 litres 10w 40 and 5 of 20w 50, if i use all the 10w40 and then whatever i need of the 20w50 is that ok, or should i not mix the oils?

Mixing oils is ok. It just alters the viscosity to a blend of the two. For emulsified oil (water in the oil) the best option is to buy 10l of cheap oil and 2 cheap oil filters. I am assuming you have one good oil filter and 5l of good oil already.

Install cheap filter and fill with cheap oil and the oil flush that you have. Ru for 15-20mins so that the engine has gotten nice and warm. Drop the oil while it is still hot (BE CAREFUL). The heat will help to rid the oil of any water/coolant as well as being diluted in the cheap oil. Fit another cheap oil filter and fill with cheap oil (no flush). Run this for a day or two. (50-100k's driving). Drop and install good filter and fill with good oil.

That will get all the water/coolant out of the engine.

cheers
Scott