There is no cumulative update to update directly from 12.1 to 13, we'll prepare it a bit later, some testing is needed. If you want to update it now, then you need to switch to Beta update channel in Studio > Developer > Update Channel. Please remember to update modules after each system update, for example:

• Go to Studio > Dashboard and update UNA from 13.0.0.B1 to 13.0.0.B2
• Go to Studio > Apps Market > Purchases and login to you UNA account if asked
• Go to Studio > Apps Market > Updates - apply all available updates here
• Go to Studio > Dashboard and update UNA from 13.0.0.B2 to 13.0.0.B3
• Go to Studio > Apps Market > Purchases and login to you UNA account if asked
• Go to Studio > Apps Market > Updates - apply all available updates here
• and so on until UNA is updated to 13.0.0 and all modules are updated to latest versions