Hello, i have a sorcerer/cleric. My question is, when  can i change spells? when they sleep, or is it something specific?

You can change your cleric spells after every long rest. You can swap out one sorcerer spell every time you go up a level.

Quote from Tim >>

You can change your cleric spells after every long rest. You can swap out one sorcerer spell every time you go up a level.

 Actually you can only change either spells when you level up because the cleric spells count as sorcerer spells and a sorcerer only "knows" spells and doesn't prepare them. So you must level up to change them.

Edit: Sorry, This is for Divine Soul Sorcerer. I missed read the part above. Yes you can prepare cleric spells as they stated.

Thanks everyone! Youve answered all i needed to know.