To remove the IDE cable you just pull up firmly on the white FOXCONN tab. If it’s stuck you can work it by pulling up on the left and right sides of the tab until it loosens.
The power cable is much harder to yank out and really takes a lot of pressure and finesse to release. It may be difficult to see but you do want to pull out that entire white block, not merely the top portion. Just grab the two sides with the wing tips and work it out bit by bit. It also helps to have a flat and thin instrument like a spudger to wedge under some of the plastic edges on this plug as you work it out, using the spudger as a lever to help pry the plug out of the hard drive.
You really don’t need to remove all four pillars, or any of them depending on the repair you’re doing. They can be pulled out easily enough, just remove any that get in the way.
Be forewarned: make sure you really really want that new battery or display replacement, because you are VERY likely to lose your Touch ID feature on your phone after taking this step. It is extremely sensitive. The front of the bracket is the point of tension that holds it in place. In my case, as I carefully used the spudger to release the bracket, the released tension shot the bracket out of the phone and the Touch ID cable popped out of its socket with it. This gave me a start but I inspected both parts and they appeared to be fine. I finished the battery replacement, and put the cable back in place only to discover: no Touch ID. Even after I re-opened the phone two more times and finally figured out how to properly reseat the bracket, Touch ID was gone. Judging by this experience the Touch ID cable/pins must be insanely sensitive – perhaps one pin was dislodged by a fraction of a millimeter? I can’t say for sure. But sadly after repeated and careful attempts to reseat it, my Touch ID is lost for good. :(