No, you absolutely cannot just switch off resentment, with only one exception: if you made a mistake, and your resentment was the result of a mistake. The thing that makes resentment last is that so often it comes from genuine hurt and genuine wrongs; it's not exactly "wrong" so much as it is unhelpful, so you're not just going to decide one day to put it behind you and that's it. It'll sneak up on you. You'll catch yourself feeling it.
But Young at Heart's suggestions are good, and I'll only add to them. The thing I'd want you to remember is patience. You will probably feel at times like you're not making progress, even if your progress is rapid. I used to drive people crazy here with my complaints that things weren't changing fast enough, that I was stuck in the same patterns. From the outside, it was clear that I was actually on the fast track and I should have been overjoyed at my luck (my wife got on board, which doesn't solve all the problems but makes a HUGE difference--I was very lucky.)
But I don't think you can avoid feeling that you should be changing faster and it's been too long, and I also don't think that's very often true. Resentment can be chipped away slowly by means like what Young at Heart has mentioned, but the main thing it takes is time. As you improve things and begin to see what's possible, resentment will slowly simmer down. You'll begin to catch yourself showing more patience, more empathy (genuine patience and empathy) and you won't always have really specific reasons why, you just won't be as angry anymore.
