Follow these steps:
If you have third-party modules installed, confirm that they are compatible with the ProcessWire version you are upgrading to. If you cannot confirm compatibility, uninstall the third-party modules before upgrading when possible, then re-install them after upgrading.
Download the latest version of ProcessWire.
Replace the directories and files htdocs/wire/, htdocs/index.php and conf/htaccess.conf from the old version with the corresponding ones from the new version
The upgrade should now be complete. In case of issues, refer to the version-specific upgrade notes documented in the official ProcessWire site.
Keep the following points in mind when performing an upgrade:
When replacing the wire/ directory, remove or rename the old one first. Don’t copy or FTP changed files into the existing wire/ directory as this will cause an error. Replacing the index.php fileEdit section
The index.php file doesn’t change very often between minor versions. Typically, you don’t need to replace this file unless it has changed. If in doubt, replace it.
The Bitnami stack’s htaccess.conf file should be replaced with the contents of the htaccess.txt file in the new version. Ensure that existing modifications in the stack’s htaccess.conf are retained. Typically, this involves wrapping the content of the htaccess.txt file in a Directory directive and adding a RewriteBase directive to it, as shown below:
<Directory "installdir/apps/processwire/htdocs"> ... ... RewriteBase /processwire/ </Directory>