How to Upgrade old version of Magento to a new version

Upgrade automatically Using Magento Connect Manager

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In the admin go to System/Magento Connect/Magento Connect Manager

Paste magento-core/Mage_All_Latest into Paste extension key to install:, then click Install

You may get a message like this(and more) in the pear window below

magento-core/Mage_All_Latest requires package “magento-core/Mage_Core_Modules” (version >= 1.1.8, version ⇐ 1.2, excluded versions: 1.2), installed version is 1.1.6

At the far right of Manage Existing Extensions click Check for Upgrades

Rows of packages with available upgrades will now be yellow.

Chose the latest version in every rows select.

Now click Commit Changes.

Now again, paste magento-core/Mage_All_Latest into Paste extension key to install:, then click Install.

Status: On successful upgrade also ,there was not changes takes place.All the files remains as it is.

Another way to manually Upgrade Magento Version

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1) Back up your Database

2) Make sure your database is backed up.

3) Setup a test site with a new version of Magento, install 1.4 using your old database and let Magento upgrade your database

4) Add in your old theme and choose in your admin backend .

5) Add your custom modules one at a time, testing each.

As for you core modifications you will have to go through them to make sure they will work on 1.4. It is a bad idea to modify core code as all upgrades will wipe out your changes.

If this doesn’t work you might want to try upgrading to 1.3, then to 1.4