farfalla95, so look at my pictures and I hope it will be helpful to you))
The first you must open the tab named "Materials" than right-click on the material you want to change:

1 by pixie Xu, on Flickr

This will open the window - you must choose the "Material Properties":


2 by pixie Xu, on Flickr

After that you must choose the tab "Maps" to change the texture of the material. You can browse your folders and apply any needed material.

3 by pixie Xu, on Flickr

For the change of location or size of your choosen texture you must work with this window. All the results you can see immediately on the screen with your 3d-model.
Also you can change sizes or the locations of the parts of 3d-models and make some othe operations with them.
Also you can convert 3d-files to the desired format for the uploading them to SH3D.
So the quick result of my texture-changing:

5 by pixie Xu, on Flickr

tuyethulis, Deep Exploration is a paying program for vewing 3-d files in a many formats. About installation - it insalls on your hard-drive like any other program, it's basics [;)]

[Note from moderator: fixed information about Deep Exploration]