Your footer lists a MacBook Pro and OS X Server; are you running OS X Server on that MacBook Pro, or are you running OS X? (OS X Server is not commonly booted on a MacBook Pro or another portable system, as that software tends to not react well to DHCP IP address changes that can arise.)
Which version of OS X or OS X Server are you running here, and having Mail-related issues with?
Guessing... If this is OS X client or the Mail.app client — and not the Mail service in OS X Server — then see if there's a glow next to the Mail.app icon in the Dock — if there's an indication that Mail.app is still running, but is not responding. If that's the case, then you can option-click on the Mail.app icon in the Dock and select Force Quit. That usually gets rid of a stuck Mail.app session.
If it does resolve the stuck Mail.app session, I'd then recommend sorting out what's going on with Mail.app before attempting an upgrade, too. If Mail.app restarts, click on the inbox mailbox you're using and request a mailbox rebuild (Mail.app > Mailbox > Rebuild). Repeat for each inbox mailbox for each of the mail servers you're using. If you have a stuck message, try logging in from the web interface on the mail server (if your mail ISP provides that), and deleting the message(s) from there. Attempting the upgrade might well run afoul of whatever's causing Mail.app to misbehave.
I am using OS X 10.8.2
I have tried to quit the mail app but nothing happens!
I have tried a lot of methods, but it do not work :/
The mail issues i have is that i can´t open mail app, but when I try to restart/take off my Mac then it cames a massage that my Mail app is open! then i goes to mail settings press the button to take mail app off, nothing happens and I try to take off my Mac again but the the same problem is happening!!!.
To confirm, you have tried many methods.
You have tried using Quit, and without success.
You cannot operate mail successfully, as it appears stuck.
To confirm what you're seeing here when you've tried what I've suggested earlier, you're using the key labeled "alt" or "option" or sometimes ⌥, press and hold that key and then click on the Mail.app icon in the Dock, then select "Force Quit" from the pop-up. (This is sometimes called ⌥ click or option-clicking.) The item to be selected from the popup should not be showing as "Quit" but rather as "Force Quit".
If you do not see "Force Quit" listed in that pop-up — and Mail.app is still running, and stuck — or if the Force Quit is visible and you can select it and it's not being honored — then there's something rather weird going on.
Next stop would be to try a shutdown.
As a last resort, a hard power-down. The hard power down requires holding the power button for approximately five to ten seconds. I don't recommend that hard power off as anything other than a last resort, as it can potentially corrupt active files and can cause problems for open applications.