Hello Julio,
I assume the phone is currently on version 6-0-1 and you are going to 8-4-1. In my experience with this large of a jump I would recommend stepping up by first going to an interim release between these two. A good release to try might be 7-0-3. Once you have that load on the phone set, then proceed with moving up to 8-4-1.
Your tftp-server statements look correct, as long as the files have been loaded into the flash root, and not into a directory. In terms of the load statement, for this phone you should have "load 7971 SCCP70.8-4-2S" as the correct statement. I also like to use the commands "no create cnf" followed by "create cnf" when in the telephony-service configuration mode. This will ensure that the system has updated the CNF files which tell the phones what version to pull down.
If you try these out and are still having issues, take a look at "debug tftp events" as this can show what the phone is attempting to get from the CME. I hope this helps. If this fixes the issue please mark your post as resolved. Have a great day.
Andy
