Its easiest to change elastomers with the stem installed on the bicycle. Press down slightly on handlebars to preload elastomer to remove pressure on stem preload wedge assembly. Remove single 4mm bolt to remove elastomer (DO NOT loosen preload extractor cap, its a T45 so you probably wont have that handy anyway). Choose your elastomer, make sure the word "TOP" is facing up toward the stem. Reinstall the 4mm bolt and tighten. DONE.