upgrading from iphone 4 os6 to iphone6 os8
Finally about to upgrade my iPhone 4(gsm) iOS 6.1.3 to iPhone 6 with current iOS8. I don't really have the space to upgrade the phone to OS 8 and sync before purchasing the new equipment so I'm thinking of just syncing the iPhone 4 as is, and let the new phone upgrade when it syncs with the cloud.
Is that inherently a bad idea? Should I (painstakingly) make more space on the iPhone 4 and upgrade it first?
Thanks in advance for any advice.