It`s a portal for beginners and intermediate guitar players, featuring video lessons from our members and a lots of other useful information for guitar players.
Since I`m not in the game from the beginning, my friend installed Seditio CMS (former Land Down Under — LDU).. 
I`m really mad on him because he didn`t start with Joomla 8), and now we face a lots of problems, such as lack of support from seditio community and lack of plugins and modifications for this site. >:( 
I would like to switch to Joomla 1.0.13 but I don`t know how can this be done? ??? can it be done? 
we currently have more than 3700 registered members so this has to be done in a right way, cause I don`t want to lose a single user or a single page in whole process of migrating! 

Any help will be apprecited.

I didn't find the right solution from the Internet. 

Explainer Video Production Company

Thank you.