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1. Basically we are not using the latest version of PHP and Joomla
2. So please download the latest version from joomla 3.9.x
3. Install XAMPP latest in your local 
4. Go to xmapp/htdocs folder,
5. Extract the latest joomla into htdocs [for ex: infovijaysite ]
6. Open it in browser http://localhost/infovijaysite
7. Joomla installation page will come. setup with the new database
8. Remove the installation folder



9. Now check the latest database with your old database. 
    9.1 you can see additionally 10+ tables are newly added in latest joomla version.
    9.2 you can see some of the columns like client_id, package_id, asset_id in few tables. 
    9.3 truncate drv_sessions table  [_session] table.
    9.4 check few table, values also changed from the old to new. possible change that too. I have taken that only table dump from new and replaced with old if the rows are same or more/less.
    9.5 verify each old table columns with new table columns. if any thing added, please add the same in your old database itself. 
    9.6  Keep remember, add those columns in the same table in your old DB and also create those 10+ tables in old DB. 



10. change the old DB name in configuration.php under your folder [ex: infovijaysite ]. 
11. ctrl+f5 or clear cache and refresh your site [point 6].


ENJOY.
I have done the same for ma own site, please visit -  www.infovijay.com



Note: But the menu may be looks diff than your old style. but your site is reborn.