Qgis - How to call another class in a plugin python for qgis?

I realized a plugin "form_1" by using the plugin builder in QGIS. Into the folder of this plugin, i have the ui_form_1.ui file. I use QT4Designer to modify the interface. After, i created another file ui_form_2.ui. I'd like to know how can i call the form_2 when i click on a button in form_1 ?

Thank you for your help.

I hope you already decided to post this question to a forum targeting QGIS.

Sorry, but i resolved the problem. Thank you.