Latest version of Asterisk issue

Which one is the latest version of Asterisk?
Asterisk 1.8 or 11?
I have asterisk 1.8.
If 11 is the latest version how can I upgrade it?
Do I have to re install asterisk again?

Asterisk 11 is the newest Long Term Support Release.
Asterisk 1.8 was a Long Term Support release as well (and still has support
Asterisk 10 is a standard release.

More info about the version on

Like you say: you have to reinstall. Although your configuration files will not be overwritten (as you don’t do a ‘make samples’, that will overwrite them.)
You have to download the source and compile Asterisk again.

You also need to read UPGRADE*.txt, and make appropriate adjustments to the configuration.