How to make a multi device application

Like the title says,how can I transform a single device application to a multi device one?..now my application work with the Fenix family,but for example if I try to run in the simulator for the Vivoactive all the Texts are out of position,because of different resolution of the two screens of course.
So how can I specify different behaviour according to different devices?
Thank you in advance.
Regards.