I just picking up one of my old 15 pages text and going through it. I come to the conclusion that a part of a scene just don't work. The conflict shouldn't be introduced that way, it adding to much tension to soon, mostly confusing, not even the writing is good etc. When you find a scene in you writing that just don't work how does you work process for changing it look like?
Usually, in my stuff, a scene doesn't work for one of two reasons: one, it's too short, as if I rushed through writing it; and two, it turns out that it doesn't belong at all. In the first case I add material, usually a lot of material, turning a two or three page scene into fifteen or twenty pages. In the second case, I cut the scene entirely. This often leaves a hole in which something should fit, just not the scene I had. So I have to write something new to go there.
I usually just tinker with it until it feels right. I never usually have a radical 15-20 page change but it usually helps enough.
If the main concern is being confusing, usually just tweaking it a bit is all it takes. If you hate all of it, just rewrite the scene and then cut it. When cutting things, I first highlight the whole scene I'm cutting in a certain color -- red, maybe -- and then I leave it there while rewriting. I only delete it when the scene is re-written. It's just a personal preference, but it helps me avoid the frustration of the Great Blank Word Doc. I hate having to write something when there's this bright, blank screen staring evilly at me.
I usually just delete the end paragraphs and try again. I'm pretty confident with my starts, but the actions come as they will, and since most scenes I write get re-written anyway between notebook and typing up they'll generally get revised anyways. It's always an end that fizzles out that bothers me in a scene.
If it's a scene that fits the story but needs to be better, I print it and use the page to highlight, make notes and play around with the language sentence by sentence. Then I go back to the computer and put the changes in. If it's a scene that serves no purpose, I save it in a seperate file just in case I find a place for it later on or in some other project.
I recently had to split a large and rather truncated version of events into two separate chapters. To make sure I didn't miss anything with a straight up rewrite, I reread and rewrote from top to bottom adding enough flavour to justify the second chapter. On the other hand if a scene just isn't working out, break it down into its base narrative components and see if you can do something completely different with the same outcome that fits the ambiance you're trying to accomplish.
If the scene feels like a bastard scene that seems to have no place where it's at, I do my best to recall what train of thoughts that lead me to write the scene in the first place, and then add in a setup for the scene which includes, or at least sparks, this train of thoughts. In many cases a scene reads wrong because you're in the wrong mood or mindset for reading it as intented, and the setup provides just that. In many other cases it's just irrelevant junk and I fix it with the Delete key.