First follow the general upgrade instructions found here to upgrade to Gazelle v12.10
Next, after you upgrade and install Gazelle v12.10 follow these steps:

  1. Login to Gazelle as Admin
  2. Go to Admin -> Entity -> Tax Code
  3. Create new Tax Codes for your branches and your suppliers
  4. Go to Admin -> Entity -> Branch
  5. Modify all your existing Branches to use the correct Tax Codes
  6. Go to Admin -> Entity -> Supplier
  7. Modify all your existing Suppliers to use the correct Tax Codes

Gazelle v12.10 also includes a new feature to print identifying barcodes in sale receipts. If you want to disable this behavior, go to Admin -> Settings, visit Client tab and untick Show receipt's barcode