mobile

Hello I recently got my xperia z2 back and saw that it needed an update, to android 4.4.4. So i did it and about 10minutes after the end of the download the phone started bugging out, the screen was acting like if it was broken. Like i would press at the bottom corner and it would launch a random thing. Now i cant even put my pin code in because its bugging that badly ! i was thinking of trying to go down an update but how do i do it if i cant even reach the settings of the phone, i think theres someway of doing it with the phone off, in some kind of safe mode but i'm not sure. if anyone knows what to do please reply !!! Thank you !!!