I have found that the only way to release the past and what no longer serves me is to forgive. I found this forgiveness prayer a number of years ago and I found that it has helped me to let go of what I no longer want to hold onto:

All that has offended me, I forgive. Within and without I forgive. Things past, things present, and things future I forgive. I forgive everything and everybody who can possibly need forgiveness of the past or the present. I forgive positively everyone. I am free and they are free too. All things are cleared up between us now and forever. Amen