Usually, you take the insole of your shoes out and put new inserts in. Many on here like Superfeet - I know REI has them. I've not seen them in an LBS. My LBS has specialized inserts - but I don't know how well they work.

I blacked 2 toenails on a ride last year. Didn't know my shoes were too small until that! Of course, it was on a day I rode 80 miles with a 105 heat index

CA