1.3.x Branch is affected by the issue described in CVE-2014-2668: DoS (CPU and memory consumption) via the count parameter to /_uuids. Upgrading to a more recent release is strongly recommended.
You can upgrade your existing CouchDB 1.0.x installation to 1.3.0 without any specific steps or migration. When you run CouchDB, the existing data and index files will be opened and used as normal.
The first time you run a compaction routine on your database within 1.3.0, the data structure and indexes will be updated to the new version of the CouchDB database format that can only be read by CouchDB 1.3.0 and later. This step is not reversible. Once the data files have been updated and migrated to the new version the data files will no longer work with a CouchDB 1.0.x release.
If you want to retain support for opening the data files in CouchDB 1.0.x you must back up your data files before performing the upgrade and compaction process.