About Installation I-TASSER Standalone Package (Version 4.1)

sir,
I am trying to install I-TASSER Standalone Package (Version 4.1).
following the steps given on ubunto O.S

This Error message appears what to do please help...........

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package I-TASSER4.1.tar.bz2
E: Couldn't find any package by regex 'I-TASSER4.1.tar.bz2'
smarla@smarla-HP-Z400-Workstation:~/Downloads$ > tar -jxvf I-TASSER4.1.tar.bz2
-jxvf: command not found
smarla@smarla-HP-Z400-Workstation:~/Downloads$ tar -xvzf I-TASSER4.1.tar.bz2

gzip: stdin: not in gzip format
tar: Child returned status 1
tar: Error is not recoverable: exiting now