On Riddell shells, you'll notice that there is a prominent ridge running across the top of the helmet.  This is where the helmet halves are joined together during the manufacturing process.  Anyway, it also has a lot of battle scars and deformations from heavy use.  I use a large flat metal file to reshape the edges and top contours.  Sometimes, if the battle scars are significant, I may even slightly file down the ridge to even out the scars, but not so much that it removes the ridge!  If there are any raised deformations from scars/hits on the helmet, I'll also knock these down with a file for sake of  expediency.

Notice the NOCSAE molding on the lower right of the helmet rear in the photo.  You can leave this on if you like, but I usually prefer to remove it as my helmets will never again be used for anything other than display purposes.

In the photo on the left, I have filed off the NOCSAE molding and sanded out the file marks.  I have also completed filing and reshaping the center ridge.

**If you choose to remove the NOCSAE molding, be aware that you automatically void any warranty, and this helmet can NEVER AGAIN be used for anything other than display purposes.  It is recommended that you do NOT sell/trade/give away this helmet after removing the NOCSAE molding, or completing any of these refurbishing steps.**