LightDM??

[SPUTNLK]

is there anyway to change the default lockscreen to LightDM ??

[SPUTNLK]

Actually i think it is GDM3 lockscreen

(ex. hxxp://1.bp.blogspot.com/-7k2I5TY3yuI/UJgzr2iar7I/AAAAAAAALmY/sJV0OHBWanI/s1600/gdm3.6-login-screen-background.png

[OmegaMK-XII]

Try:

dpkg-reconfigure gdm

and choose lightdm