Squeeze the lemons and put the juice in a 1/2 gallon pitcher, making sure to strain out the seeds. Make sure all seeds are gone from two of the lemon halves left over after squeezing, and put them in the pitcher. Add the sugar and warm water and stir until everything is mixed well and sugar is dissolved. Fill pitcher with ice and stir to melt it and cool the lemonade or just add cold water. Serve in a tall glass over ice. Be sure to remove the lemon halves after 1-2 hours or they will start to turn the lemonade bitter.