When is the best time to take puppies off of mums milk ?

I have got 6 puppies who are now 4 weeks old and there mum doesn't want to feed them as much anymore as they are getting to big for her i have given them full fat milk when they cry because there hungry and now give them scrabbled egg yokes every couple of days but when is it best to put them on to puppy food and am i giving them the right thing at the moment any help would be amazing thanks !!!!