The answers that tell you to be completely objective and professional, because that is how you are supposed to perform your job, are spot-on.
However, I can't help but feel that the personal aspect is being skirted a bit.
If you do your part correctly, if the other person is completely professional, it should go smoothly, perhaps, but when talking about someone's job, their career, and their ability to earn a living in a way that is not positive, people often take that emotionally and personally, even if, objectively, they shouldn't. One reason is because we're human. Another reason might be that, if you're dealing with someone who has professionalism or performance issues, that is sometimes a result of them not being as objectively professional in their jobs as they could be.
I only mention this because I don't want you to see answers that say "you do your part, and it will be fine," and then you get blind-sided if it doesn't go well.
How does that change your preparation? It doesn't. You being professional insulates you from adverse results about as well as you can be insulated. The degree to which your friend might not be able to separate that friendship from professional duties, or recognize that your new role requires you to do this, is something that you can't really control. In that regard, it does you no good to try and manage something outside of your control (their reaction), beyond doing the best you can with the part that you can control.