Fuel lines

I've brought replacement fuel lines( 7) from HEL , has anyone changed them out and what should I look out for?

If you are referring to the ones in the egine bay, then pretty straightforward job. Might need some penetrating oil as the existing fittings may be a bit tough and banjo bolts are a bit softer than std bolts and you really don't want to round one off.
The only ones that will be difficult will be the injector end ones, as access is limited. I'd suggest pulling the injectors (although this can be a pain as well) and buying new injector seals (cheap enough on ebay).That way you can remove the injector from the line out the car. Put a new seal on the injector and push them back in. You can remove the old rock hard seals carefully with a sharp knife.
If they don't come in the kit you'll either need new copper washers for the banjo bolts, or you can re use the old ones after first heating them up witha  blow torch until they are glowing and drop them in cold water.
It doesn't matter which output from the metering head goes to which cylinder.

Ok thanks , I did get injector seals as well but I'm told there a sod to remove 

soak the injectors with wd40, brake fluid, for few hours days even, before you try popping them out,  how i did on all my cars and believe me its not a simple job, as they can be proper tight, is to remove the rocker cover, and then fit a sturdy plate, nylon block along edge of engine cover and lever the injectors out. if the old hoses are goosed then you could pull on them at the sametime togive some leverage.  check your routing of new injection lines, and make sure you have the right fittings, as the hoses come in 2 sizes