This process is pretty simple, so here's the rundown.

Right click on Persona 4 Arena Ultimax in your steam library. A popup menu will appear, now click on "Properties..."


Now go to the "Betas" tab.


Now you need to type the code "p4auopenbeta03" (No quotation marks).


Click "Check Code" and a blue button should appear beneath the code, click it to opt into the beta.


If the blue button doesn't appear, instead click on the dropdown box above the code and select "open_beta_3". Your game should now update.

You're done!

• You can now skip intros at the beginning of matches without negatively impacting the connection.
  
• You can now freely play any stage without it greatly impacting performance.
  
• Try to use a wired Ethernet connection when playing online. Wifi is super inconsistent.
  
• Some player rooms are still "ghost rooms" and are bugged and unjoinable. To find consistent matches against other new players, try using the Persona Fight Club discord server. (Steam doesn't let you link discord servers, just Google it)
  
• The beta sometimes crashes or desync's mid match, but these bugs are infrequent. This will likely get patched in the official release out of beta.
  
• Ranked PSR stops increasing so quickly after about 100 matches, and after C rank you can only rank up by playing against others up to 2 places away from your rank. For example, if you were in B rank you could rank up by fighting anyone in C C+ B B+ A ranks. Masters can only rank up by playing against other Masters, same goes for Grand Masters and Kings.
  
• You can hold A and B during an All Out Attack to automatically get all 18 hits without having to mash buttons.
  
• Check out the Dustloop for more information about the characters' toolkits, as well as combo guides for each of them. https://www.dustloop.com/w/Persona_4:_Arena_Ultimax_Remaster

That's everything. Post a comment if you're having trouble accessing the Beta.