Hello!
Deciding on whether to use "which" or "that" has to do with whether or not the information after it is essential.
If the meaning of the sentence changes by taking the phrase out, use "that."
Example:
The boy that wore a red hat broke his arm.
The boy broke his arm.
(If we take out "that wore a red hat," the sentence could now refer to any boy...not just the one in the red hat.)

If the meaning of the sentence won't change if you take the clause out, then use "which."
Example:
Vogue magazine, which has 2 million subscribers every month, includes advertisements from a variety of brands.
Vogue magazine includes advertisements from a variety of brands. (This statement is still true. The "which" clause is unimportant added information.)

I hope that helps. I'm available if you'd like any follow up.