I started by watching some YouTube videos on how to replace the agitator. The best video was from Appliance Pros and included a link to order the new part. The price was cheaper than Amazon. I used standard shipping and received my new part in about 2 days.
The hardest part of doing the replacement is pulling out the old part. Videos will show a couple off tricks using cord string or straps to pull off the old one. I was able to get my fingers under mine, and with a good snap, it popped out. I cleaned up the old spline and slid the new part on. Easy peasy!