I believe the official way is described here:
https://github.com/papampi/nvOC_miners

In case you don't feel comfortable with git and want just your T-rex updated:

T-Rex miner is located in: /home/m1/NVOC/mining/miners/T_Rex/recommended, this directory is a softlink to recommended version.

- login as m1
- "nvOC stop"
- download newest t-rex to
- "cd /home/m1/NVOC/mining/miners/T_Rex"
- mkdir I believe newest is 0.8.6 so do: "mkdir 0.8.6"
- "cp /t-rex.new.version.tar.xz ." (this will copy new t-rex to current directory, don't for get the dot .)
- "cd " (0.8.6 in this case)
- "tar xvfz ../t-rex.new.version.tar.xz" (unzip the tarball packet)
- "mv t-rex ccminer" (rename t-rex to ccminer)
- "cd .."
- "rm recommended" (remove softlink to old version directory)
- "ln -s 0.8.6 recommended" (create new softlink to new version)
- nvOC start

Writing this from top of my head, hopefully got it right.

--
Tigel