I realize this topic is fairly old, but thought I would help clear this up for anyone else who may have the same question. Although I don't support Bitmain or any of their subsidiaries (for many reasons I won't get into), here is the answer:
After logging into AntPool, you will automatically land on the Bitcoin mining page. If you are mining Bitcoin on AntPool, you should stay on that page, click on "Settings", then edit your Sub-Accounts Bitcoin address in the "Wallet Address" field. If you are also mining Litecoin on AntPool, in the top left corner, you will see a small arrow next to "Bitcoin" where you can click to open a drop-down menu (upon clicking, you will be able to switch between any of the AntPool mining pools). In this case, you would click on "Litecoin" and will be redirected to the AntPool Litecoin mining page. From there, you will again click on the "Settings" link and fill in the Litecoin address where you wish to receive payouts.
I should also mention that there are MUCH better mining pools out there for both Litecoin and Bitcoin (in my personal opinion anyway). One of the biggest reasons is that AntPool does NOT include transaction fees in payouts to miners when using their PPLNS, PPS, or SOLO methods (Bitcoin transaction fees have historically accounted for up to ≥30% of the Bitcoin block reward as seen
here, and more recently ~7% of the block reward). Taking that into consideration, I find it hard to believe so many people are mining Bitcoin on AntPool! In addition to that, I don't believe anyone should support a pool that is owned and operated by a company who so strongly supports the Bitcoin Cash fork anyway..