From LifeType Wiki
LifeType 1.2 packs an incredible set of new features and improvements, but please consider a few things before diving into the upgrade process. Users wishing to upgrade to LifeType 1.2 from a stock installation of LifeType 1.1 with only a few customized templates will have an easy upgrade path. Users who have done any customizations or who depend on certain plugins for their sites please read carefully this section.
The best way to keep our customizations in sync with the work done by the project team is by either using Subversion to keep our local instance updated with the project Subversion Repository, or by running our own Subversion server and using SVKConfig to keep our internal server synchronized with the project's.
Unfortunately this is not the situation in most cases and changes have been performed ad-hoc without any kind of control, so upgrading to new major releases might end up being a painful process.
Also please consider using "upgrade" releases that the project makes available whenever a maintenance release is made. These releases (labeled for example lifetype-1.1.1-upgrade-1.1.2' to indicate that this package only allows to upgrade to 1.1.2 from 1.1.1) include only the files that were changed between the base release and the newest release. This means that we will only have to check the files that are included in this package and not all of them.
Unfortunately upgrade releases are only available when upgrading versions within the same branch, so there is no upgade package from 1.1.5 to 1.2. but only between 1.2.x releases.
Users who have done heavy template customizations to their sites will need to compare all templates and see what changes the project team performed to accomodate some of the new features. As far as templates are concerned, there are three main areas:
- Admin templates - Summary templates - User templates (and user-customized templates)
The best way to go about upgrading your customized templates is by using a tool that will allow you to compare the changes between two files and between to folders, but it's altogether a complicated process.
The development team recommends to try to isolate your changes to CSS files.
Upgrading plugins and code customizations
Code customizations and custom plugins is also an area that needs to be looked into when upgrading to a new release. While the plugin interface has not basically changed (plugins in LifeType 1.2 work in the exact same way as they did in LifeType 1.1), the API has experienced a fair amount of changes.
Code written by project members includes class documentation in the code to be processed by tools such as  (recommended by the project) or phpDocumentor. If these tools are not available, a most recent version of the API documentation will always be available at http://www.lifetype.net/api.
It would be impossible to provide a list with all the API changes in LifeType 1.2, so the recommended way to get our custom code updaded to work in LifeType 1.2 is by actually testing it and see where it fails. When it fails, please consult the API, the developers mailing lists (plog-general and plog-svn) and the support forums at http://forums.lifetype.net.