How do you cut off part of a mesh you don't want? I made a clothing mesh in the program  Sculptris a open source sculpting progam and then exported the mesh to Blender 3d. When I made the mesh in Sculptris I made alot mistakes on the pant leg and I do not like the way it looks  so I want to delete the part of the pant legs and redo it. However,  I do not know how to delete parts of mesh I do not like.  I am still much a newbie to Blender, I understand most the basics of the program but I am still learning all the tools in Blender.  I am sorry this such a newbie question.  Can you please explain it to me of what is the tool to use and how to use it?
Switch to Edit Mode.

You can do this by going to the Tab (Don't know what to call it) near the bottom, most likely called Object Mode and clicking it followed by Edit Mode. You can also press the Tab key, which is the shortcut.

All of the vertices should be selected, which you can tell if they are orange. We don't want all of the vertices selected. Press A to deselect all the vertices, it should go from orange to black.

Now you need to select the area you would like to delete. Press B and drag over the area desired. Make sure to rotate around the model since it won't select the vertices on the other side (and I don't know how to fix that but it should work either way)

After the vertices of the desired area has been selected press X and then click 'Vertices'

Hope this helps.