Upgrade Joomla 3 Website

I’m ready to move my existing Joomla 3 site to the latest stable Joomla release while preserving the exact look and feel of every page. The template should carry over untouched, so when the upgrade is complete visitors shouldn’t notice any visual difference—only smoother performance and improved security under the hood.

Functionally, the site relies on just a couple of key extensions. They must work flawlessly after the migration, whether that means updating them, finding compatible replacements, or tweaking code to eliminate conflicts.

To make this a clean, low-risk transition I expect:
• a full pre-migration backup and a staging copy for testing
• the core upgrade carried out on the staging server
• extension updates or equivalent solutions in place and tested
• a thorough post-migration check of front-end display, admin functions, and URLs
• final deployment to the live server once everything matches today’s design and functionality
• concise documentation of steps taken and any code changes applied

Please outline your approach and estimated timeline so we can get started.