One way to accept or "to let go" is to explore the belief/value that is stopping you from letting something go because you hold that as "TRUE".
It can be for example...
1 We shouldn't be wasteful.
2 Things should be fair.
3 If I remarry, then I will dishonour him (In a scenario when someone have lost their husband for example).
Once aware, we can "challenge that" (CBT Cognitive Behaviour Therapy style) or defuse from it (ACT Acceptance Commitment Therapy style). You cannot "TRY to let go" in my opinion because letting go is in essence "not trying". So "letting go" in my mind is more about "unlocking" or through deep understanding and validation rather then "doing" which many are trying to do. I often find that people are constantly saying, "Yes, I am trying to let it go but I can't!"
Mindfulness practice will help one to be less judging and more "perceiving" and from this "state of mind", letting go is easier in my opinion.
If your want to read more on ACT Acceptance Commitment Therapy, I would recommend a book written by Dr Russ Harris The Happiness Trap. You can search for it in our Self Help Bookstore tab above on our page.