[Sony Xperia T2 Ultra] vrutantdante:
First of all you need to know your device's bootloder is locked or unlocked for that type *#*#7378423#*#* in dial pad then go to service info >configuration and check for bootloder unlock allow

If it say yes then it's unlock

If it says no then it is locked

Do as follow for unlocking the bootloder

You need your device's IMEI number and a password for unlocking your bootloder

You can get your password by following link

Do step by step

http://developer.sonymobile.com/unlockbootloader/unlock-yourboot-loader/

1)switch off your device and open flashtool(download from following link)

2)select the unlock bootloder and connect your phone with flash mode by keep pressing vol. Down button and connect the cable LED light will turn green and then it will off

3)enter Your device's IMEI number and the password you got from Sony

4)click on unlock

Now your bootloder is unlocked so now can install custom recovery like XZdualrecovery,TWRP,CWM (unfortunately CWM is not supported in 5.1.1)

For installation of recovery you need to download full Rom from Xperifrim or other source and convert it into Ftf file

You need 1) kernel which have recovery pre-installed like doomlord's kernal for D5303 device for Android 4.3

2)For recovery which work with it just download latest version of XZdualrecovery for T2 ultra from thread and download the Release file (there are 2 file which are located there one is release and second is installer)

Download it on phone and move it on place whare you can find it easily

1) Now switch off your phone open flashtool

2) select flash sign and select fastboot mode

3) Now connect your phone with computer in fastboot mode by keep pressing vol.up button and connect the cable and LED light will turn blue

4)select doomlord's kernel file for flashing (it'll be on img format so select img from file type)

And flash it

5)Now disconnect your phone and boot it. When Sony logo appear and then keep pressing vol.down button alternatively it will boot you to CWM recovery

Now touch is not working... You can move upper option by volume Up button and downward option by volume down button for selecting the option press power button

Select install >install from SD card or external SD(where you placed a file)

Select flash and recovery will install then for back to exit there is (/) sign which can bring you to previous menu then exit from recovery by pressing vol.up button and power button holding together until it vibrate 3 times now your phone is power offed

6)Now click on flash button on flashtool and select flash mode

Then choose your latest 5.1.1 rom and now do as instruction or your data will lost

1) first you choosed a rom to flash now it will show a dialogue box that how many files are in that rom for flash now on right top you have 2 check box ( data and cache) uncheck both of them.

2) under that you have Exclude box which have check boxes too

Now check all boxes(system,some other things) but make sure only kernal remain uncheck

Now click on flash button

It will ask for connect your phone in flash mode by holding vol.down button and connect the cable

Now it will flash only kernal file all other files will remain same

Disconnect your phone and boot it until Sony logo appear and keep pressing vol.down button alternatively .... It will boot to TWRP recovery which is Easy to use and touch is also working now for get back to normal boot just select last option reboot and it will your

(while you want to enter into recovery keep pressing vol down button alternatively until LED blink green or some other colour.after it blinked you can't boot to recovery)

Hit thanks button if this helped you... And ask if you stuck at somewhere

This was simple tutorial and you are doing this all at your own risk I am not responsible for any damage of your device.