Just so you know -- the EASIEST way to switch is to drain and refill. Not recommending it; just letting you know.

Assuming you don't want to drain, you have two options:
1. Fast, cheap, but risking green hair and stains.
2. Slower, more expensive, but little risk.

If you're not worried about a few bluish green stains on your pool, or about green hair on family members (affects blondes and possibly 'grays') -- go with #1.

To go with fast and cheap, simply
1. Run your filter 24/7.
2. Maintain low chlorine levels (1 - 2 ppm) with small repeated doses of bleach. (2 cups)
3. Gradually raise your pH level -- a little at a time -- to 7.6 - 7.8 by adding soda ash in small repeated doses to the skimmer. (Not at the same time as the bleach!) (1 cup at a time.)
4. Then, gradually raise chlorine to shock levels (~5 ppm with no stabilizer), by small repeated doses.
(doses are for a 10,000 gallon pool)

Do this over the period of a week, and most of your copper will be gone. If you use cal hypo shock -- not a whole bag at time -- it will work even better. (1/2 cup)