Like Flashing_Expert said, until now there is no way to install kitkat (4.4) on Xperia L with locked bootloader. The latest stock rom available is running jellybean (4.2.2), so if you want to have kitkat, you will need to install a custom rom on Xperia L, what is impossible to do at this moment because of locked bootloader restrictions.
Maybe there will be a way to do it in the future, but that depends on Xperia L developers work. Xperia SP, for example, has Cyanogenmod (custom rom) and others custom roms for locked bootloaders.
Last edited by Abruzini; 13th May 2014 at 03:13 PM.