i have lightroom on two computers , can i deactivate one and put it on another device.
my dell desktop broke and i wanna use my lightroom on my other computer i have but its not letting me because i already have it one two .
Assuming you are talking about Lightroom 6 or Lightroom CC (what version are you talking about?), you have to use the Creative Cloud application to Sign Out on one computer before you can install it on another computer.
In addition to the suggestion by djpaige, you might be receiving an option related to the exceeded limit on the third machine while trying to activate Lightroom and you can choose the option "sign me out of all all other computers or devices" to deactivate from both the older machines
and then, you can sign in to the ones on which you want to use it.