You should lose weight

You are overweight.
1 You should lose your weight.))
2You need to lose your weight

+++Yana

Valery, we don’t say that

YOU SHOULD GET SLIMMER is a prediction, not a suggestion. “If you follow this diet consistently, you should get slimmer within three months.”

the context can easily change a prediction into a suggestion -To join our fashion runway team you should get slimmer by the next season

In your mind. That sentence was made up by you to accommodate your point, but it’s not natural. We would say “If you want to be one of our runway models, you(‘ll) need to lose weight/slim down by next season.”

In other words, we tell people to LOSE WEIGHT or SLIM DOWN, but not to GET SLIMMER - it's not idiomatic.

Valery, your translation is still incorrect.