Something like this ought to get you going...
import os
import arcpy
from arcpy import env
# directory containing rasters to be renamed
RASTER_DIR = 'C:/MyRasters/'
env.workspace = RASTER_DIR
for raster in arcpy.ListRasters():
# get the raster name and file extension
fileName,fileExtension = os.path.splitext(raster)
# do some shenanigans to rename the file
# based on your sample raster name, fileNameParts would look like
# fileNameParts[0] = m
# fileNameParts[1] = 3609922
# fileNameParts[2] = nw
# fileNameParts[3] = 14
# fileNameParts[4] = 1
# fileNameParts[5] = 20100425
fileNameParts = fileName.split('_')
compactFileName = fileNameParts[1] + fileNameParts[2] + fileExtension
arcpy.Rename_management(raster,compactFileName)