With Mailify, you can store your account data and your campaigns in the Cloud which is activated by default (To make sure it is activated, check that there is a green point next to the cloud). If you would like to use your account on a different computer (but not at the same time), you just need to activate the cloud in the second computer.
In order to be able to use the same data on more than one computer at a time, you can buy other users for your account. To do this, see our guide here.
Go to "Settings" (on the right, click on your name and then on the cog). Go to "Synchronization" and you will see the computers that are linked to your account. Here, you can delete those that you don't use.