Your clients version is .5 versions behind ... 2.6. is now 2.6.8.
It is supported for security fixes only now and will soon slide into 'legacy' ... no longer supported.
To have exactly what they have, suggest doing a site backup ... that includes code directory, an sql dump of the database, and the moodledata directory. Then restore to a server of your choosing. You will have to change the site URL on your version.
That's called 'migration' ...
Once you have their site up and running (by another domain name) on a server you might spend some time in learning how to upgrade.
'spirit of sharing', Ken