I want to yell at my sister to stop crying
Are you kidding? Why do you want to yell at her when she's crying?
Because it annoys me, she needs to grow up. She acts like a baby
You should not be raising your voice to your family members. You need to behave in a more tolerant and understanding way towards your family.
She's a spaz and if I don't yell at her, she'll never change.
I don't think yelling at someone who is already crying is wise. You should have a conversation with her to find out what is upsetting her.