Hello, they all mean the same, however, yup and yep are never used in writing. They are more casual ways of saying yes in a conversation setting. The other casual ways to say yes are: yeah, yip. Also common to say "All good".

Literally they all mean the same thing "YES". However, "yup" and "yep" are only used in an informal setting as you can't use it in formal or professional writings. They're synonymous to "yes" in informal writing. To sound formal, polite, and professional please always use "yes". Best Regards!

Yup, yep and yes all mean the same