This tutorial assumes you've already set up your Web3 account and bought Sets. If you haven't set up your Web3 account, you can check this tutorial here on how to get started on TokenSets. If you haven't bought a Set, you can check this tutorial here on how to buy a Set.
How to sell
Click the Set you want to sell in one of those lists. This will navigate you to the Set's landing page. Once on the Set's landing page, click "Sell".
Input the amount of Sets that you want into the sell input. You can also choose Max, 1/2, and 1/4 of what you currently own. Once you put in how much of a Set you want to sell, click "Preview Sell".
View the order confirmation and make sure that everything looks correct. If everything does look correct, click "Submit Sell".
A transaction should show up using your Web3 wallet of choice. Confirm your transaction to allow the transaction to start processing.
The transaction will start processing. This usually takes about 30 seconds when none of the transaction parameters are changed. If you change the gas amount, it may lead to longer transaction times or lost transactions.
Once you transaction has mined, the sell order should either say success, still pending, or failed. You can always check the Etherscan link that comes with the transaction to make sure that the transaction has going through.
Once the transaction succeeds, you should have successfully sold your Set.