The following was posted by Blizzard Entertainment regarding the latest PTR for Overwatch:

To participate in the public test, you must have an Overwatch game license for Windows PC attached your account in good standing (i.e. it hasn’t been suspended or banned).

Step 1: Restart the desktop app.
Step 2: Navigate to the Overwatch tab on the left-hand menu.
Step 3: Select “PTR: Overwatch” from the REGION/ACCOUNT drop-down menu.
Step 4: Click “Install” to begin the installation process.
Step 5: Once the PTR client is installed and updated, click “Play” to begin!

Note: In order to access the PTR, you must have installed Overwatch and logged into the game at least once. If the PTR is not available for you after following the steps above, trying logging into Overwatch, exiting the game client, and then launching the PTR again.

Q. On which platforms is the PTR available?
A. The PTR is available on Windows PC only.

Q. What regions are eligible to participate in the PTR?
A. Accounts from all regions (excluding China) are eligible to participate; however, the PTR will be hosted on our Americas region. As a result, if you plan to play the PTR from a region outside the US, please anticipate lowered performance and increased latency.

Q. Is there a cap to how many players can participate on the PTR?
A. The PTR can currently support 10k concurrent players (or players logged into the PTR at the same time). If we happen to reach this cap, any new players attempting to log in to the PTR will be placed into a queue.

Q. What languages will be supported on the PTR?
A. The PTR is available in all supported languages, though some content may not be fully localized yet.

Q. Will any account progress from the live game transfer over to the PTR with me, or do I need to start from scratch?
A. A copy of your account from the live game will be transferred over to the PTR automatically, and all progress will transfer over with it (level, unlocks, stats, etc). Please note that this copy is pre-made, though, and based on an earlier snapshot of your account. As a result, depending on when you last played, your PTR account may not be as up-to-date as your live game account.

Q. Will any progress I make on the PTR transfer over to the live game?
A. No. Any progression earned during the PTR—including levels, achievements, stats, skill ratings, loot boxes (including rewards from loot boxes), currency (including Competive Points), and cosmetic items unlocked with currency—will not transfer over to the live game.

Q. Will I be able to purchase Loot Boxes on the PTR?
A. No. All real-money purchases are disabled on the PTR.

Q. Where can I share feedback about the upcoming patch content?
A. This iteration of the PTR is intended to make sure the upcoming patch is working correctly before it’s released, so we’ll be primarily focused on uncovering major bugs and technical issues. Though you are still welcome to share your feedback through our normal channels, it’s unlikely that we’ll be able to incorporate changes based on PTR feedback in this patch cycle.