Where to begin!?!
You need to be an Aeroplan member to even consider using an eUpgrade. Your friend cannot simply give you "a" credit. They could nominate you as a beneficiary of their credits. That member - who would be prestige, elite or Super elite - would be the one who applied - through their account - to have you upgraded. They will need your record locator number (6 digit alpha numeric code) for your flight and your booking has to have your Aeroplan Number on it.
There are lots of threads on eUpgrades - it would be advisable to invest some time to read these...