When should I switch to size 2 nipples

It says the months on the package. I don't remember what 2 is. I think it's 4 months and up?

3 or 4 months.

Or when your baby is getting frustrated that they're not getting enough.

it will say on the package but my daughter hated going to a faster nipple...so until she turned one she was on slow flow lol.

3 months