From 1.x to 2.x
---------------
Upgrading from CDN integration 1.x to 2.x requires applying a new core patch.
Alternatively, there is now a new type of CDN integration that does not
require a core patch, instead it relies on the theme layer to alter file URLs.
It is slower and won't be able to alter *all* file URLs, but it is easier to
use. When the module detects that the patch is not applied, it will
automatically fall back to this mechanism.
Also note that the core patch is already included in Pressflow!

The recommended steps to update your Drupal site are:
1) Copy the 1.x core patch (patches/drupal6.patch) to the Drupal root directory.
2) Revert the 1.x core patch:
    patch -p0 -R < drupal6.patch
3) Disable CDN integration at admin/settings/cdn.
4) Update the CDN integration module code.
5) Copy the 2.x core patch (patches/drupal6.patch) to the Drupal root directory.
6) Apply the 2.x core patch:
    patch -p0 < drupal6.patch
7) Re-enable CDN integration at admin/settings/cdn.

The ImageCache module patch has remained unchanged since version 1.x. When you
did not apply the core patch and thus want to rely on the theme layer fallback
mechanism, you don't have to apply the ImageCache module patch either.
But when you update to an ImageCache version that's newer than 2.0 beta 10,
you will have to apply the alternative patch: patches/imagecache_6--2.patch.


From the Parallel module (1.0) to the CDN module (>=2.1)
--------------------------------------------------------
In February 2011, the Parallel module was merged with the CDN module since the
CDN module had received a superset of the Parallel module's functionality.
Hence it no longer made sense to maintain the Parallel module.
This is a guide on how to migrate from the Parallel module to the CDN module.

1) Download and install CDN module version 2.1 or newer.
2) Download Parallel module version 1.0 (its latest release).
3) Run update.php. This will migrate the Parallel module's settings to the CDN
   module.
4) Visit admin/settings/cdn/details. You should see a translation of your
   Parallel module settings to the CDN module's format here.
5) Visit admin/settings/cdn. You can enable the CDN module here, or run it in
   debug mode to give it a try.
6) Disable the Parallel module at admin/build/modules.
7) Uninstall the Parallel module at admin/build/modules/uninstall.
   
If you'd prefer to stay in control and would like to enter your settings
yourself into the CDN module, that's also possible. Then you only need to
perform steps 1, 6 and 7 and finally go to admin/settings/cdn, where you can
then  enter your desired configuration.