Is it possible to root Xperia M2 (android lollipop 5.1.1)

I've always wanted to root my phone but didn't want to loose my warranty. So recently my 1 year warranty ended and now I would like to root my phone but I'm not sure how to do it and this is the only forum that i really trust.
I have the latest android version installed (5.1.1) and my phone is the Xperia M2 D2303.
It says that I can't unlock my bootloader "Bootloader unlock allowed: No"
If someone could explain how to root it please do so.
Thanks in advance :D