How to upgrade drupal modules?

Question

In my case I'm upgrading the memcache module,though there's a README.txt but it seems not operable :

1. Install the memcached binaries on your server. See http://www.lullabot.com/articles/how_install_memcache_debian_etch
2. Install the PECL memcache extension for PHP. This must be version 2.2.1 or higher or you will experience errors.
3. Put your site into offline mode.
4. Download and install the memcache module.
5. If you have previously been running the memcache module, run update.php.
6. Apply the DRUPAL-5-x-cache-serialize.patch from the patches folder that
   comes with the module.  Version specific, so use DRUPAL-5-6-cache-serialize.patch
   if you are running Drupal 5.6.
7. Start at least one instance of memcached on your server.
8. Edit settings.php to configure the servers, clusters and bins that memcache
   is supposed to use.
9. Edit settings.php to include either memcache.inc or memcache.db.inc. For
   example, $conf['cache_inc'] ='sites/all/modules/memcache/memcache.db.inc';
10. Bring your site back online.

Especially step4, does it mean just unpack the module and replace all stuff in original directory?

My current memcache version is 5.x-1.9 and there's 5.x-1.10 available,but I don't see it available at admin/logs/updates

Answer 1

Step 4 means that you remove the old module directory completely and only then unzip the new module code. You don't want any remnants of the old code.

Answer 2

Also note, that

1. Not all module developers think the same about dot releases: sometimes 1.2 and 1.3 are major rewrites or come with completely new features, themeable-functions, pages or APIs.
2. Not all upgrades are compatible with others. Sometimes you cannot update module B to 1.4, because of its dependency with A, A seems not compatible with 1.4 (yet). Drupal does not support dependencies on versions.
3. Major releases imply (but do not guarantee) incompatibility, or even complete rewrites: Upgrading from 5.x-1.4 to 5.x-2.1 might force major rewrites of custom code, including your theme.
4. Security updates often are dependent on earlier releases: 6.x-1.2 might introduce new features (that you do not want, or wish to ignore), 6.x-1.3, can be a security-release that requires (some of the) the changes in 6.x-1.2 to be available. You must then either fiddle around with patches, or go trough that feature release anyway.