Sgt KIA is talking about editing the textures in photoshop.
I will try and explain why it is looking strange...
After you have finished making your model in a 3d program, you have to map the model by unwrapping the mesh.
This process is known as UVW unwrapping. You take your 3d model, and on a 2d plane, you have to move about the polygons to make your model flat.
If you have ever made a box by cutting a piece of paper into a "t" shape, with 6 rectangles and folding it into a box, then it is the same as that, but backwards. You are unfolding your model.
Here is a quick picture I found on google image:
That is actualy quite a good example.
Imagine your player model is the box on the right. WHen it is unwrapped, it looks like the thing on the left. You can take that image into photoshop, and start to paint your texture on it. You could cover one of the red squares with a metal texture, then when you aply the texture to your model, that red square would look like metal.
Now, every time you unwrap a model, especialy complex models, the resulting uvw map will never be the same! Also, perhaps a differnt artist made the pilot legs, that the one who made the sentry legs. They may have differnt methods for laying out a uvw map.
You can see this when you look at the pilot and sentry textures:
Pilot:
Sentry:
As you can see, the textures are layed out completley differntly! I would say the Pilots map is much better layed out than the sentrys map. With the pilot, you can eaysily see what is what, but with the sentry, his legs are somwhat squashed, and you would realy need to have the model open in a 3d program to see what is what.
So, when you aply the pilot's texture to the sentry's model, the sentry uses it's uvw map to work out how the texture should be fitted to the model. There is no guesswork here, it just aplies the texture as it is layed out from the uvw map, so the texture is applied all wrong!
So, you must either just edit the sentry texture, or as Sgt KIA said, paste the pilot texture over the sentry texture in photoshop, and cut out each part, and rotate, and resize them to fit where the sentrys stuff is.