How and where?

Avoid sending a text message about the break-up at all costs. It is most respectful to convey the decision face to face rather than via chat or phone or email.

If you are unsure how your partner might react, a public space like a cafe or restaurant might be a safer alternative as it automatically restricts any out-of-control behavior. If you are sure about your partner's emotional control, it might be safe to do it in a private place where it is just the two of you.