When you do a back up for your old iPhone 4, you can restore that on your new iPhone 6. Once you have tested your new iPhone 6 and confirmed everything is back on it. You can have your iPhone 4 reset to factory settings and give it to your friend.
Here are the instructions directly from Apple website:
Follow these steps:
If you paired an Apple Watch with your iPhone, unpair your Apple Watch.
Back up your iOS device.
Tap Settings > iCloud. Scroll down and tap Sign Out. In iOS 7 or earlier, tap Delete Account.
Tap Sign Out again, then tap Delete from My iPhone and enter your password.
Go back to Settings and tap General > Reset > Erase All Content and Settings. If you turned on Find My iPhone, you might need to enter your Apple ID and password.
If asked for your device passcode or Restrictions passcode, enter it. Then tap Erase [device].
For further details and other processes please refer to the Apple support website found here.
If your friend is going to be using it on the Rogers' network then she will need to user her own sim card. If not, than the phone will need to be unlocked.
Re: Upgrading iPhone, can I give my old one to a friend?
Honestly there isn't much else to be done. If she will be activating the phone in her name under a ROGERS account, then she just needs to get a SIM card. Once she has your phone she needs to activate the SIM card with your phone, go through the standard credit evaluation, etc, and that is it.