Late last week, ASUS began pushing Jelly Bean to the Transformer Prime, and it followed up by doing the same for the Infinity this week. That's great for users running stock systems with locked bootloaders, but if you don't fall into that camp, then you get no OTA love from ASUS. Now, though, they have made available the full stock ROMs for both tablets.
The ROMs, which are Android 4.1.1, can be flashed using any custom recovery - simply unzip the download and drop the contents onto your device's storage partition. From there, flash it just like any other ROM.