USE TWRP for the zoom
datare format can say whether it is advisable to make a data format to my xoom to move from the 155 to the 160.
Short form tutorial ---
Root Xoom - if you are on 155 you have done this
install TWRP recovery -- check the thread in Developers forum for Xoom for links and instructions - this recovery seems to work well with all of the ROMS I've tried -- and is tested to work properly for the the 160 nightly for 4.2
Download the 160 nightly and the 1209 dated Gapps ( note.... due to technical issues with the Xoom this is the only one that will work properly.
Follow the instructions for EOS4 in the dev forum.
read, read, read the forums
going from 155 or earlier REQUIRES a complete wipe
"Perform a full wipe (read Factory Reset) prior to installing this over ANY ICS based rom."
install and enjoy..