Suppose you have a glass of water and it's filled halfway with hot water. Then you dump a half a cup of salt in it and you stir it up. The salt represents your bad Kamma. Now, usually most people wouldn't want to drink this water, it's pretty salty isn't it? Take this salty water, and you pour it into a bathtub, and then you put buckets and buckets and buckets of pure water in the bathtub, and keep on adding pure clean water, until eventually the bathtub is full. Now I wonder whether it will taste as salty? What do you think? You probably will be able to drink that. So, understanding the benefits of good Kamma, and taking joy with our good Kamma, helps us understand that we may not be so burdened by our past Kamma. It becomes more and more diluted. As we develop our mind, some of the past bad Kamma that comes to us may be seen more as an opportunity, because we have a more developed mind to deal with it.
As far as being freed from bad Kamma is concerned, I don't think there's a special technique that we can use to magically get rid of our bad Kamma. But as far as the burden and worry about past Kamma goes, it's a matter of developing our mind in beneficial qualities and developing confidence in ourselves. To feel the ripples of our bad Kamma and to be able to see them as opportunities to develop ourselves. Dukkha can be a burden or it can be an opportunity, it depends on our perspective. It's a matter of changing our view of Dukkha. Then our Dukkha is not so much of a burden, but a means to develop more compassion, a means to develop more wisdom, a means to develop more motivation to develop ourselves, understanding that we need to develop ourselves so we can deal with the Dukkha of life.
It's a matter of looking at our worry and learning how to note the worry and see that it is a burden. Also, the more we worry about it, the fewer chances we have to put more water in the bathtub. So, developing more confidence in ourselves to deal with Dukkha, seeing it as an opportunity, and developing much more good Kamma. And remembering "Good luck, bad luck, who knows?" Who knows about some of our bad Kamma, it may be good Kamma, it's all a matter of perspective. Some of the difficult times I've had in my life, when it was happening it was bad Kamma, bad luck. But who knows? Maybe I wouldn't be here and interested in the Buddha Dhamma if I hadn't had some of that stuff. Sometimes a lot of the people who come here have had Dukkha in their life, and the Dukkha has awakened them to the need to do something about it. We can't do anything about the past and what has already occurred, but we can certainly develop the capacity in the present to deal with the present, and to protect ourselves in the future by developing ourselves in qualities that enable us to deal with the ripples of our Kamma.
As far as a technique to overcome all bad Kamma, it is written that we have to become enlightened. So, try to develop a motivation to become fully enlightened and free from Kamma.