Since staff hadn't mentioned, but who don't want to download the whole game here is the most simple way.
Things you need:
1. Current wow with 5.4.2
2. Wow.exe file from here https://mega.nz/#!JRMGgbbB!D0b0G9BMp...Vklv9blzYsEw-s
What you need to do:
1. Open your Mists of Pandaria folder
2. Move your downloaded Wow.exe file there and overwrite the current one (which is 5.4.2)
3. Launch new one wow.exe file.
That's it, gratz you have 5.4.8 version of wow!
P.S. if you face some critical errors or anything else that your wow crashes, make sure you go to place where your MoP folder held, right mouse button on in (on folder) - > Properties and make sure its NOT checked to "Read only" (aply to all folders and sub-folders).
Also some people got all keybinds removed, in order to bring them back, in WoW when you in game, go to Keybindings and there is checked opton "Character specific keybindings" uncheck them and your keybinds will be back.
About crash when you enter world. There is possibility that you have some outdated addons which makes your wow crash, try bacup them and remove from wow folder, it might work.