for some reason, people always end up calling me willy.
anyways, i can't remember how i wrote that tutorial thing, it was a while ago. but firstly, you have to understand the few types of things that can screw up your verticals.
1) barrel distortion or pincushion distortion, this is
lens characteristic, you can only correct it post process. easiest way to understand this is to look at verticals/horizontals through a fisheye lens, or examples. for normal wide angle lens, or uwa, you will usually have milder variations of barrel distortion.
2) how parallel your camera sensor is to the vertical - easiest way is to go to a wall column, where you have two verticals near to each other. alternative is to think of looking up at chopsticks memorial up close - when you look up, verticals converge - this is called the keystone effect.
for your picture, i am not sure what #1 is, since i am not a user of your lens.
#2 is present in huge quantities there - this is a problem and limitation of photography. even if you use a tilt shift lens here (mainly for the problem of keystone effect), you will probably not be able to correct that much. i couldn't say for sure though, i have had a brief encounter with a t/s lens once only.
so you have angled your camera way upwards, probably something like / relative to the vertical |.
verticals do not always need to be corrected, as i wrote.. the keystone effect can be used to great effect to emphasize the height of a building, bring out a mood of "looming", etc.