This is seriously not hard.
step 1. loosen screws
step 2. pull off grip (you may need to stick them in hot water for a few minutes to make the plastic more pliable)
step 3. cut down poles using hacksaw or better yet, pipecutter
step 4. put grips back on
step 5. tighten screws
step 6. ??????????????????????????????
step 7. Profit.