Upgrading to Drupal7-Consider this before moving
Before upgrading your website from Drupal 6 to Drupal 7 you need to analyze whether your site actually needs upgradation and also you need to assess if the contributed themes and modules that are already installed can be upgraded. You need to prepare a list of all the non-core themes and modules that are installed and check which ones have Drupal 7 compatible version and which ones do not. You need to follow more basic steps of planning, preparing, upgrading, and then finally testing. Create regular backups during the upgradation process. And also always remember that you can upgrade your site only to the next higher version. In case you are having Drupal version 5, then you need to upgrade it to Drupal 6 before you can think of upgrading it Drupal 7.
For the contributed themes of your site, you can set a filter on the basis of compatibility and get the themes that match the upgraded version of Drupal. Similarly, for the custom themes, you need to check and ensure that the custom theme is compatible with the new version and can be done by visiting the theme guide posted in the Drupal authorized website. At any point, in case you find the themes and modules are not compatible to the new version then you might just consider not to upgrade immediately and might also think of contributing towards making those themes and modules Drupal 7 version compatible.
Before upgrading also check for special upgrade instructions, and also ensure that you have completely removed the entire old module directory before you move the new module directory. Then you need to enable the new module and run the update.php in spite of the fact that you have run it once while you were upgrading the core. Create continuous backup of all database and flies so that at any point if you are stuck, you can revert back to the latest update.
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