Slice your Mesh up with Boolean

*edit* on reflection I dont advise this method as it is more messy than I first thought

I missed this great Blender modifier for  ..ever ..until now! Boolean

So I made some boots in blender and want change the cut - but the mesh is awkward to remodel.  In Blender there is a modifier that lets you slice through an object with another object (in this case a plane to cut through my boots)

To use Boolean I position my plane to where I want to slice through the boots

Then Choose modifier>boolean

Below is the resulting mesh, the original boots are still there but I have hidden them

You will need to tidy up the area of the cut but that's no problem. Happy days!