Yes, I did find the location where you can trigger the upgrade. Google has several questions regarding this, but I was able to find it myself.
But where to actually find these "cosmetic changes" to the tower "in the flesh"?
When I upgraded my courtyard, a real nursery station appeared back where Cassandra is training / left of where you fullfill requisitions. After the upgrade of the main tower I checked out Skyhold and did find nothing new or changed. 
Left of the upgrade beacon in the tower.
It's on the battlements that surround the garden. You'll see an "!" on the mini-map when you're close.
Your name lies OP or you'd a seen it 
Your name lies OP or you'd a seen it
@Thread: Thank you guys. I think the term "main tower" was a bit misleading here. There are several structures within Skyhold that are higher and bigger than this particular tower.
Your name lies OP or you'd a seen it
The problem is that I'm somewhere between 100 and 500 meters big, so looking at such small things beneeth my feet is difficult. 
You can run, and you can swim...but I'll get ya, land or see:
Retour en haut