If your license was purchased through a retailer (Thomann, Amazon, etc.), please create a BorisFX Account first. Then login to your account on borisfx.com and redeem your license: https://account.borisfx.com/redeem
Use the redeem code provided by your reseller.
You'll then see your license and serialnumber in the "licenses" section. Click "Show more" to see your third party serial redeeming options.
Then download and install BorisFX Hub: https://account.borisfx.com/downloads
Start BorisFX Hub and login. You'll then be able to activate your new license using the serialnumber provided in your BorisFX account.