You don't say what phone you have and what OS version you've updated to, so I'm having to take a guess here. If I'm wrong, please post again with full information - remember that we only know what you tell us, and there are a lot of different devices and OS versions out there.
So, I'm going to guess that you have a recent HTC, such as a One, and have updated to Sense 5.5. That would explain the loss of ability to choose the lockscreen: HTC removed that in Sense 5.5. Instead in 5.5 the lockscreen gains the ability to add widgets: open the lockscreen and scroll to the right and you are faced with a "+" icon to add widgets. And you can keep scrolling right and adding more widgets.
On mine I don't have the option to add BlinkFeed, but I don't actually use Blink and have disabled as much as I can, so that might be the reason. So I suggest just giving it a try and seeing whether it is there.
I have to admit that I personally like to use a different wallpaper for the lockscreen, and since I've not found how to do with with the Sense 5.5 lockscreen I've gone back to using WidgetLocker instead.