How to downgrade freepbx if upgrade fails

Hello folks!
I want to downgrade from freepbx 2.8 to 2.7.
Where can I find the files to do this in the server?
Where are they stored?

if you didn’t do a backup you aren’t going to be able to downgrade as there are schema changes that would need to be reversed which a full backup would do.

what issues are you having with 2.8?

I am new to Asterisk and freePBX and am using the both for my final year project and in the course of this i have encountered the following problem.
I am trying to connect three asterisk boxes with different versions of Freepbx(2.7 & 2.8) on them.
Haven created the Peer and USers on both boxes and created the outbound routes for both boxes i encountered a problem, the box with 2.7 connects call to the box with 2.8 but the box 2.8 does not connect, and i assume that this has to do with dial rule on the 2.8.
Can someone tell me to write a dial rule for four digit extension number in freepbx 2.8 as my extension on the all start with 3XXX and the other box 2XXX.

Am considering downgrading as a possible option if i do not get anyhelp.