It means he increased the distance between himself and the closest competitor behind him. (I assume you are talking about a running competition or something in the Olympics). To lead means to be in front of the others. To increase the lead means to widen the space between you and those running after you. (can also be in swimming or another sport) If it is not sport it can also be in politics for example in the election when one candidate is getting more votes than another one.Therefore he is ahead (winning the election)

Lead is one of those words in English that can have several meanings and pronunciations. For example. Lead can be pronounced 'Leed' as in "He was in the lead," Or 'I grabbed the dogs lead and took him for a walk." In the second example a lead is a rope that you use to tie around your dog when you walk him. Otherwise Lead can be pronounced 'Led' as in, 'There was some lead in the batteries but it's leaked out." I hope that helps.