This tutorial is a basic guideline. Before doing anything BACKUP YOUR SITE! You can use Akeeba backup or a similar program. Make sure that your backup works perfectly. It is important if something going wrong to recover your website from the latest version.
All Bonus Themes joomla! templates are full compatible with the latest version of Joomla! 3.x. So the procedure is simple.
Step 1: Check if your server supports the joomla requirements or not.
Ensure that your server accepts the technical requirements of Joomla! CMS.
Step 2: Check the compatibility of all the extensions with Joomla 3.x
Before doing anything check if your extensions are fully compatible with Joomla! 3.x
Step 3: Update all joomla! extensions to be compatible with Joomla 3.x
If you find any extensions compatible with Joomla! 3.x, upgrade them. At this step you must not upgrade the template. Only the extensions.
Step 4: Delete all joomla! extensions that are NOT compatible with Joomla! 3.x
In case you find extensions that aren't compatible with Joomla! 3.x, uninstall them.
Go to "Manage Extensions" and choose "Components". Delete those components that are not compatible with Joomla 3.x and do the same with "modules" and "plugins".Make sure you did not delete any Joomla stuff! Do NOT delete what you before in Step 3 have upgraded. Be Careful! If you complete this step it's time to get to Joomla! 3.x.
Step 5: Update Joomla! 2.5 to Joomla! 3.x
A. method (recommended)
Download and install the file "Joomla_3.X.Χ-Stable-Update_Package.zip" from here: joomlacode.org.
This is an easy step. So go to the component "Joomla Update" and select the global "options" icon (in the right top of your screen). Select "Update Source" tab and then change the "Update Server" settings from Long Term Release (LTS) to Short Term Release (STS) and save. Now go back to Joomla! update and you will see that the 3.x version is available! Click UPDATE and in a few seconds your site will be on Joomla! 3.x.
Step 6: Last but not least update the remaining extensions
Now it's time to install the Joomla! 3.x version of Bonus Themes templates. Finally check if everything gets on well and don't forget to create a new Joomla! 3.x backup. I suggest you to save the backup file locally.