How we change what others think, feel, believe and do
When you recall past happy events, talk about them using imperfect verbs that allow for continuation, rather than the 'over-and-done-with' perfect verbs. For example, say 'I was enjoying' rather than 'I had enjoyed'.
When recalling unhappy events from the past, reverse this order, using perfect verbs rather than imperfect verbs.
In a different interpretation of the title of this article, you could also change what you remember or the associated emotions. Make happy things happier and unhappy things not as happy.
Hart (2013) asked subjects to recall positive past events and then assessed their mood and happiness. He found that those who used verbs in the imperfect tense (as opposed to the perfect tense) subsequently reported a greater happiness and more positive mood. The implication from this is that the 'completion' of the perfect tense blocks a more detailed recall that includes accessing of positive mental states.
This emphasizes how the language you use has a subtle effect on how you think and that any positive words would likely make you feel more positive. For example, using active verbs is more likely to evoke emotions than using passive emotions.
A corollary would be that people recalling past negative states using the verbs in the perfect tense would experience less discomfort than those recalling using the imperfect tense. This gives an additional technique for reducing unhappiness in recall.
A further use of this understanding is to use imperfect or perfect verbs when talking with other people based on whether you want to evoke or quell emotions.
Note that memory is not like a computer disc, recalling exactly what happened. It involves much reconstruction and can be completely changed, as seen with many law-court witnesses. This also allows for modification of how you feel about past events and adjusting this to increase happy memories and reduce sad memories. To some extent we do this naturally, for example with the 'rosy glow' of nostalgia that conveniently avoids past difficulties.
Hart, W. (2013). Unlocking Past Emotion: Verb Use Affects Mood and Happiness, Psychological Science, January 2013 24, 19-26