How to upgrade Joomla
This tutorial will show you how to upgrade Joomla 
Upgrading 1.5 from an existing 1.5x version
From Joomla! Documentation:
It is risky to upgrade a live site without testing the upgrade process first. So before upgrading the live site you need to set up a test site which is as close as possible to the configuration of your live site, then test the upgrade on that. When you are happy with the process you can apply it to the live site (having taken a fresh backup of the live site first, of course).
Review the release notes for the new version. When upgrading from a version that is not the most recent, review release notes for the prior releases.
Step 1: Download the upgrade file
To download the most recent patch package and to obtain the MD5 hash:
- Proceed to the Joomla Download page.
- Locate the row that matches your current installation version.
- On that row, select the patch package (zip, tar.gz and tar.bz2) that is most convenient for you.
- Verify the download using the MD5 hash listed in the right column on the same line as the package you selected.
To find the MD5 hash:
- On the Joomla Download page, click on “Download other Joomla 1.5.x packages”
- Click on the bold text in ‘Release Name’ column. For example, if you want to find the hash for 1.5.9 to 1.5.10 patch, click on ‘Joomla1.5.10updates’.
- On the next screen click on the ‘Files’ tab, where you will see the hash for each package.
If you have questions about these instructions, read the Additional Information below this table.
Step 2: Backup your site
Before you actually upgrade, you really should make a backup of your site. Backup your existing Joomla site files and store all the files and database in case something gets messed up, you wont have any problem reverting back.
All upgrades should be first tested on a copy of your site before being applied to a live site.
Step 3: Install the upgrade file
There are different ways of installing a package file depending on your particular circumstances. If you have difficulty with one of these methods, then simply try another.
- Alternative 1: Unpack the package file on your local computer then use an FTP client to upload them to your site.
- Alternative 2: Use an FTP client to upload the package to your site, then use a terminal session (eg. SSH) to connect to your site and unpack the files there.
- Alternative 3: If your hosting provider gives you access to your site via some sort of web control panel like CPanel or Plesk, you can use the control panel file manager to upload the package, then use a terminal session (which might also be available via the control panel) to unpack the package file and overwrite all changed files on the server.
Step 4: Check your live site to make sure it is working correctly
Don’t assume that the upgrade will work flawlessly just because the test upgrade worked. Check to make sure that nothing untoward has happened. It could be that differences between the live site and test site platforms will bring out a problem that you did not notice during testing. If you find a problem and it cannot be resolved quickly you might have to rollback the upgrade using the backup copy you created in step 2.
Hopefully all will be well and you can relax. If you have any questions before, during, or after the upgrade then please ask them on the Joomla! 1.5 Migrating and Upgrading Forum.
