here is generic upgrade project that has little to NO production downtime
when we do upgrades, we do it on a copy of production and when ready we replace production with new copy and import out of sync customers/orders..there may be more depending on your shop....
=== checklist .doc'ing
- identify all 3rd party modules and obtain their 1.7 compatible zips
- identify core changes (mentioned above), you should also identify template changes (.tpl's).
- .doc existing overrides
- select new feature rich theme, we like Leo themes but there are lots of others
- review existing hosting, most age just like your shop. it's best to get new hosting account and move to that rather than try to have old hosting upgraded
=== pre upgrade
- build a test copy of your production shop, then back this up so you can refresh your test system until upgrade completes. hopefully your hosting allows php level by domain/subdomain so you start out with php7.2. if not find new hosting.
- uninstall 3rd party modules
- make sure overrides clean
- up php max execution time to 'large', 600 or 1200...
=== upgrade
- back up this test system so you can restore if upgrade fails so you do not have to uninstall moudule/override again
- perform upgrade
- install/configure modules
- apply core changes
- install configure theme
===shake and bake until prod ready
== Production installation
- create a new copy of production to be used for historical purposes
- import customers/orders from old shop to new shop
- copy new shop to production or if new hosting (recommended) switch dns
happy upgrading
el