lighten up
verb
- (cause to) become lighter, easier
- begin to handle/approach in a less intense way than the previous handling
- stop being so serious
Wiktionary
verb
- To make (something) or to become less serious and more cheerful or casual; to relax.
“I wish he'd lighten up a bit and realize that we were only joking.”
“The mood at work has been tense, so he's looking for ways to lighten it up.”
- To lighten (something): to decrease its weight.
“Near-synonym: slim down”
“He can't get any more power out of it [his drag racer], so now he's looking for ways to lighten it up.”