(be new) •
It's a blessing. Used when someone have something new (new haircut, nails, clothes, car, shoes, objects etc. Etc.) It means enjoy your new things.
Probably come from the prayer the religious jews say when they wear new clothes.
The cashiers in stores also say this when giving you what you just bought.
"זה מה שקנית אתמול? תתחדשי!"
"That's what you bought yesterday? Be new!"