You would download the autoloader file https://mega.co.nz/#!Io9BQAJR!LIiqOk...KtlDk1AuLPvtsg
for whatever version you wanted to install. Use desktop software to make a backup before upgrading.
Backup your Z10 with Link.
Download Autoloader File.
Turn off the Z10.
Run Autoloader.exe (May need to enable Admin priv)
When “connecting to Bootrom” appears on system connect Z10 to PC and turn on device.
Wait for process to finish and phone to reboot.
The update will wipe your device, so you can either restore all the info from your backup through BlackBerry Link or just start fresh if you want.
You also want to make sure that the OS version matches your handset model (STL100-4) and most have 2/3/4 in the same file, but not always.
It's a lot easier to upgrade with the Z and Q then with any of the older models.