Update testlink 1.8.3 to 1.9.3

[konica_testlink]

I have no experience of testlink installation or configuration. I am only an user of testlink 1.8.3, which is connected to Jira 5.1.x,
in our setup we have more than 2000 test cases and also hundreds of bug entry.

now, if I want to update this testlink to a newer version (for example 1.9.3), what should I do?
how to take backup before so that if I damaged any link, I can return back to the current setup.

If anyone have ideas, please provide me.

Thanks
-Konica