Upgrading GitLab from 6.2 to 8.5

Looks like the installation was done by Bitnami method by an ex-employee
I am looking for an easier installation method for future upgrades. Is it easier to do by Omnibus installer?

System information
System:         CentOS 5.8
Current User:   git
Using RVM:      no
Ruby Version:   1.9.3p448
Gem Version:    1.8.24
Bundler Version:1.3.5
Rake Version:   0.9.2.2

GitLab information
Version:        6.2.1
Revision:       f2a77a8
Directory:      /opt/gitlab-6.2.1-0/apps/gitlab/htdocs
DB Adapter:     mysql2
URL:            http://xx.xxx.com
HTTP Clone URL: http://xx.xxxx.com/some-project.git
SSH Clone URL:  git@xxxx.xxxx.com:some-project.git
Using LDAP:     no
Using Omniauth: no

GitLab Shell
Version:        1.7.1
Repositories:   /opt/gitlab-6.2.1-0/apps/gitlab/repositories/
Hooks:          /opt/gitlab-6.2.1-0/apps/gitlab/gitlab-shell/hooks/
Git:            /opt/gitlab-6.2.1-0/git/bin/git