Hi sorry for late answer I hope it is still relevant to you.
You can order a device online easily it's quick and very convenient plus no activation fees.
Unfortunately as far as trading in a device to Fido the store Fido is your only outlet but there are other ways than trade you can sale.your device yourself Kijiji etc. Maybe for more money.
You can maybe mail it with battery out in the package for the Fido store to review it for trade and give you an estimate trade amount but you would still need to go to Fido store (Maybe a parent of yours can go to Fido store) If you then want to proceed with an upgrade device there.
Fido will only accept a trade in exchange for new device activation. They would deduct the trade off the new phone sale price but remember that in store service cost activation will be payable 25$. postpaid plan and all.
I hope it helps you decide,