How do I properly return an item to an eBay seller for a refund or partial refund?

[dana]

I tried Googling this first, I promise. I just want to do everything correctly because I'm not eBay savvy.

-I ordered an item. It's the wrong item. I open a case with PayPal resolution center, wanting a full refund.
-The seller responds and asks me to return the item, then she'll send the correct item, and issue a partial refund to cover the shipping cost.
-I agree. I'm not sure if there's a certain process I have to put this package through.

So do I just send it right back (with a tracking number) and that'll be that? Do I have to involve PayPal somehow, since I filed a claim through PayPal?
Oh, and when she said she'll pay for return shipping. Would I just tell her how much shipping cost? I'm gonna get a paper receipt from the post office. How exactly should I handle that?
I feel like I should already know this stuff. =/

[Linds]

First you contact the seller, if the seller doesn't respond within five days then you file a claim with paypal or ebay. So you did one step wrong. So since the seller did contact you, then you mail them the wrong item, and they'll send you the correct item.

[Jessica]

Contact the seller and work on the sitaution together so you both know where its going, etc.