I have wordpress 1.5 and I want to upgrade to 1.5.1.3 but there are no instructions for that update, and from searching the forums I saw that I need to update to 1.5.1 and then to 1.5.1.2 and then to 1.5.1.3. But I can't find where to download 1.5.1 or 1.5.1.2. Where can I download these upgrades?
http://static.wordpress.org/archive/
But you don't need to upgrade sequentially. Each download is a full install, so if using 1.5, just download and replace your current installation with 1.5.1.3, then run wp-admin/upgrade.php.
Yes but there are no instructions for it. There are only instructions for 1.2.x to 1.5 and 1.5.1.2 to 1.5.1.3. I found sequential instructions here in the support forums.
And the archive only goes up to 1.5.1.
Unless you're trying to update only the files that have changed, the instructions are the same.
I'm assuming my themes and plug-ins would then have to be re-added?
Follow the 1.5.1.2 to 1.5.1.3 instructions (you can leave wp-contents/ as is):
http://codex.wordpress.org/Upgrading_WordPress#Upgrade_1.5.1.2_to_1.5.1.3
But do make sure to run upgrade.php at the end, as there were a few changes since 1.5 to the options table that need to be added.