How to relock bootloader?

[XEL]

I unlocked mine way back when it was on Android version 4.4.2.. Now there's an update to 4.4.4. but I can't update it since I have an Unlocked Bootloader right? :(. So.. Is there a way for me to lock it back? 

My Phone are Xperia M2(D2305)

[AI13]

I tried to relock my xperia XA by using xperia companion 

WARNING - THIS PROCESS WILL DELETE ALL USER DATA

To do so-

1. connect your device in flash mode then launch flash tool

2. then click on BLU(boot loader unlock) after process again click BLU and then click relock

3. Your device may not boot aftrer showing sony logo for a few seconds 

4. Go to xperia companion > software repair > check the box "my device cannot be detected">click next>select android 

5. And it should start repair after a few minutes  

6. After process disconnect your device and reboot it, it will take longer than normal reboot

[Ralkeon]

I'm trying to relock a Xperia 10 plus but I receive a WARN on blu click:

"WARN - Your device cannot be relocked"

someone had more luck with this?