New Post: Blog package repair

Hi,
The only way to upgrade the Blog package is:
0) Backup site - this is important step :)
1) Backup Blog data stores files (if your site is XML based, then files are located here \App_Data\Composite\DataStores\Composite.Community.Blog...xml )
2) Uninstall Blog package
3) Install new Blog package
4) Restore Blog data files

You say that the package disappeared from the "Installed packages", so you can't uninstall the package. Each package has its unique ID, and information about installed package you can find in folder "\App_Data\Composite\Packages\<package id>\". Check out that the blog package folder "\App_Data\Composite\Packages\303b7865-055b-4fe7-a429-907b32bb6776" exists and the folder should contain next files:
Binaries/
info.xml
installed
package.zip
uninstall.xml

If the folder or some its files are absent, then you will not see the package in "Installed package" and need to restore these files. If you have site backups, try out to locate missing files.