I lost hot water so I changed both elements, my water got hot for about a week and now it keeps tripping unit off, so I have to remove cover and reset button, what is the problem and how do I fix it? It is a Bradford White 50gal?

Make sure the thermostat is actually hard up against heater to get accurate readings. If it is giving problems, you either do not have it hard against tank or it has failed and needs to be replaced. When they get too hot too often the spring gets soft. Best to simply replace.