need help with making a low poly mesh from a high poly mesh

i made a high poly mesh in sculptris and i have brought it into blender so i can make a low poly mesh of it then bake the normals onto it but in sculptris it runs smoothly but in blender it runs slow
so if anyone could help me the would very help full



You could try the Decimate modifier, which will calculate new vertices and reduce the polygon count. Results may only be visible in Object Mode until it is applied.

Here is good tutorial.