Okay so previously on the home screen ,I'd press the menu button- wallpapers- lock screen wallpaper and select my image to set as the lockscreen wallpaper.I can't do that anymore after the lollipop update. And also battery has been draining out like crazy after I updated it. This needs to be fixed.
Note: This is a partial answer and is meant to solve the Lock-screen wallpaper issue only.
One way of changing the lock-screen wallpaper in CM 12 (the update for OnePlus) is:
Go to Settings → Themes →tap the wrench icon in your current theme → scroll down to Lockscreen Wallpaper → Pick Image (choose the image) → tap Back button/key once and tap right icon to apply the custom theme. Done.