This is how I did it anyway, I suppose this is the way.

NOTE2: If you just open SAI2 and try to save, it is obviously grayed out since you have no file open, make an empty canvas and you'll see the save interface normally - I was stupidly almost pulling my hair out seeing the option grayed out after doing everything right not realizing I had no file open. NOTE: It still says preview version - this is normal, it just means the program is not the final release. Run SAI2, you can now save files as normal. Download the certificate and put it into the SAI2 folder OR Documents/Systemax Software Development/SAIv2 (I can't remember which, I originally put it in both and I don't remember which it has to be) Input the system id and your license number and certificate download password - the latter two will be in an email you got when buying the regular SAI. Check your system id from SAI2 (Other -> System ID in the top bar of the Sai2 program) and copy the number it gives you It will warn you that you cannot save or something for lacking the license. The program does not have the old Sai shortcut icon either. Unzip and run it, it does not have an installer. The technical preview just means it's a beta version. Download the 'technical preview,' probably the 64bit version if you are on Win10. The page might seem sketchy, I just find it charmingly old fashioned.) It has been years so I don't how it happened specifically. FireAlpaca is the free Digital Painting Software that is available in 10 languages and compatible with both Mac and Windows. Have regular SAI license (->You must have bought the regular SAI to use SAI2, and in the lower part of the page there should be a link to purchase a license.

Paint tool sai 2.0 brushes