How to convert from high poly to low poly I'm making a game in the unity engine and for my models i'm using blender 2.6. The thing is that i'm pretty new to graphics design (modeling, sculpting, etc) and by following some tutorials i've managed to make some very high poly meshes for my characters with the sculpt editor, the meshes have about 1.5M - 2M faces and of course a game character should be less than 30K faces so the game runs smoothly with good optimization on an average pc.

my question is how do i translate the details of the high poly stuff to low poly meshes (7k - 30k faces), i've heard about uv unwrapping and stuff but i'm not sure what is the process to follow.

i don't mind if the recommendation is very hard and for advanced users because the primary thing i want to do with this, is to learn.
One way to reduce mesh density is the decimate modifier, however for the workflow you want (creating a game asset) I think you want Retopology. 

This is a workflow which gives your more control over the final result, however it will take longer as it is a manual process.

Some helpful addons and built in functionality for retopologizing your mesh:


Surface Snapping (feature)
Shrinkwrap modifier (feature)
Bsurfaces (bundled addon)
RetopoFlow (addon)


Some tutorials and reference material:


Bsurfaces demo
wiki page on retopologizing


After you have a lower topology mesh you can bake normal maps etc. to make it appear more detailed than it really is.