Move from a raspberry PI B+ to a Pi 3

Is it possible to move a running libreelec system on a PI 1 B+ to a PI 3

just by dropping the tar file for a rpi 2/3 into the .update folder then moving the sd card from the PI B+ to the PI 3 and rebooting, so it would go through an upgrade procedure

or do I need to do a full re-install on the PI 3 ?

I've just discovered the manual upgrade tar files don't appear to available anywhere anymore so whole idea may be a non-starter anyway