Main and general steps you can find in those articles and knowledge bases.
https://confluence.atlassian.com/adminjiraserver/upgrading-jira-applications-938846936.html
Be careful regarding checklist
https://confluence.atlassian.com/adminjiraserver/upgrade-checklist-966063320.html
If you will choose installer method follow this
https://confluence.atlassian.com/adminjiraserver/upgrading-jira-server-installer-938846937.html
I can recommend you go through this way:
6.3.7 -> 6.4.14 -> 7.0.11 -> 7.13.3 -> 8.2.1
thank you very much for that !! that helps a lot. Do you have a idea of a planning ?
What you mean with planning?
I would like to make a provisional schedule for this migration but I do not know how long it takes for this
First do this on test environment - then you will know what problem you can expect on production and how much time it will take.
Based on my experience - if you don't have any special add-ons and customizations - it could take on production whole weekend (better start at Friday afternoon after bussiness hours).
ok I understand better. So the weekend would be enough to migrate to version 8.2.1 ?
If there will not be any serious problem - then yes.
Hello @jean houssin - I encourage you to heed these very wise words from @Petr Vaníček - "First do this on test environment - then you will know what problem you can expect".
This is not a trivial change you are making. You will likely need to work out problems in your test environment (which should be a copy of your production environment, not a vanilla installation) at several stages. Practices this until it is a well-documented and smooth operation. Then you will be better prepared with a comprehensive plan, fairly accurate time estimates, and be able to focus more on the unexpected things that will happen during your production outage.
~~Larry Brock