this might help you get started

http://docs.elgg.org/wiki/Main_Page

In quick summary:

1.  I am not sure about the various versions of Elgg and not exactly sure why you don't know which version you are using, but you can see the version in the Readme.txt file in your elgg root folder (At least it shows for version 1.8).

2.  A theme is treated like a plugin.  Copy your theme folder into <ELGG ROOT>\mod folder (which is where all plugins and themes go).  Log into Elgg, then click on Administration.  It should automatically appear in the list of plugins.  Click activate.  Refresh your site and the new theme should be active.

NOTE:  If you are new to Elgg, I wouldn't mess around too much with themes until you get a good feel for Elgg.  Buggy or incomplete themes may not surface some of the functionality of other plugins.  Use caution - it can render inaccessibility to your site as well.  If you choose to go forward, be aware of this.

Better yet - if you want to see the version outside of the app - open up the file "version.php" in the Elgg installation root folder.

Hi.I 'm newbie in elgg. I tried to download a theme. And follow the approiate procedure. And I've found the theme list in the admin tool. But I cannot make it enable. Pls tell me what is wrong? ( I use 1.7.8 version )