Errors while upgrading

I am using Dolibar 3.1.1 since long time ago.
I descide to upgrade my Dolibarr to the latest version or other stable version.
unfortunatly I can not do that !
there is some issues in relation with the data base that i can not understand.
1st Question : How can I migrate from a very old version to the latest?
2nd Question, I have alerady the Database, how can I use it with a latest version if i descide to install Dolibarr 8 in another hosting space

Just install files of dolibarr 8.0
Dolibarr will detect your database is too old and will ask you to make the upgrade of 3.1 -> 3.2 then 3.2 -> 3.3 until you are in 8.0
To use your install into another instance, if you want to migrate to a paying service like dolicloud or novafirstcloud, the support will load your old data for you (see https://wiki.dolibarr.org/index.php/Migrer_vers_DoliCloud)
If you have your own hosing, just make a search on Restore on wiki.dolibarr.org to have tutorial to restore an instance on a new server.

Dolibarr detect the data base but failes in migrating data

Nobody is devine or can read your logs or error messages. This is needed to go further.