How to do LODs?

You would have to export the original LOD 1, 2, and 3 and then import each of them into blender. Then you append your mesh to each of them in blender and decimate your mesh accordingly.

Decimate is found by clicking the little wrench tool in the top right hand corner of the screen, then add modifier, you will see a list of modifiers, choose decimate in the generate column. There is a slider at the bottom called ratio. When you move that to the right it will decimate your mesh, removing verts and faces. It can only be used in object mode and it can be hard to see what's happening to your mesh until you choose apply and then go back to edit mode. I often switch to Solid from texture so I can see what is happening a bit better. Too much and the mesh will start to collapse and end up with holes. It takes a bit of practice to do the 2nd and 3rd lods then the shadow lods, by then the mesh could end up a real mess. I always use the highest mesh then save it as the 2nd & 3rd as I reduce the polys. Check each mesh in edit mode to see if there are any gaps or if the mesh has become misshapen I also have a look at the UV maps to make sure both are the same while I do this. Another way to reduce polys is to use the Delete Doubles on the mesh tools tab at the bottom. this can take a lot of weight from the mesh without spoiling it and give you the next lod along. I have also found that it seems to help when decimating the 3rd meshes, maybe because these is less to pull around once that is done. If you have a lot of tris faces (triangles) you can click mesh at the very bottom in Edit mode then scan up until you find faces and try, Tris to Quads. This will change the faces to oblongs or squares instead of triangles and can also help reduce the mesh size. If your lods look ok check that all your UV maps are the same on each lod, I did this last week; forgot to update the second uv map and the object looked terrible in the game until I remembered.

You mean seams at the ankles? It's perfectly normal that your mesh gets a little destroyed in lower lods. It won't matter because lower lods are used when you zoom out the camera in game real far away. You won't see much detail from that distance.

hi! does the original mesh have only one mesh group as well? bare in mind that if a mesh is divided into a certain way, your mesh should be like that too.

if that's not the issue then you can try exporting the original mesh and replace only the bottoms with it.

Does the mesh you are replacing the original with have 3 groups? When I changed a mesh with 3 groups to two I had to guess, using the fact that the 3rd had a invisible shader, which groups to re assign the mesh bits too. To separate a part of the mesh while in edit, highlight the parts you want to separate on the UV map because its more precise. Then press P Blender will ask how you want to separate, click the top option. Now you will be left with an extra peice of mesh you have to append to a new group, ie, lod 1, 2,or 3. Whichever you choose you must make sure it fits all the UV maps with no edits. make sure all the UV maps are named uv_0 before doing this as it will mess them all up. For the next part I think I will leave it to the clothes experts to advise you as I have only done this on objects. Good luck