I made a model of an animal in the blender. I started by doing the geometry and then applied the modifier multiresolution to be able to later sculpted. At this moment the mesh has almost 8000 vertices, but the faces are not properly organized. What I wanted exactly was a way to restructure the mesh so that the model can be used in animation easily, but without losing quality. Retopology is an option?
The best (and proper) way is to retopologize the model (use snaping on face) with subsurface-workflow and adding the detail by baking a normalmap with the highpoly model.
Then you'll get a animatable mesh with fast rendering details.
If you just want your mesh to be simplified, you can use the decimate modifier and change the amount of total faces without modifying the shape too much.
I'm not sure if this is what you want, but you can press Ctrl+E and then select "Un-Subdivide". This will reduce the number of vertices on your model by a lot.