So only patches for SP13 and no direct/complete installationIt seems to be that way, yes. SP13 isn't available for download, not sure why.
So i'll have to install these patches on SP 12 installation?Yeah, that should get you to SP13. Make sure you read the README before applying the patches though and ideally you should make backups and test this on a test/dev system before doing this in live (if you can). In either case give yourself a backout option to roll back if things either don't go well or break afterwards. The usual "being a good sys admin" type of stuff really.