Increasing weights should be done by % not lbs. If you are looking at 5 lbs you should add no more than 1 lb. When you feel you are able to move up in weight add 1lb all the time, then if you feel as though you are able take the extra weight easy add more sets before you add more weight, make the most out of each weight movement, as the heavier your weight gets, you will never be able to drop down from lets say 15lb to 5lb ever again to deform the tissues. Your unit will be tougher, you have after all trained it.