Changing text in donation-widget?

I want to change texts in the sidebar donation-widget. I want to edit all texts like "raised" - "choose an amount" - "make this donation"

and also the text in the dropdown-menu "once" - "daily" - "weekly" - "monthly" - "yearly"

as I have to translate them in another language. Here you can see the widget in the sidebar http://www.progettourbano.org/

Do is there an easy way to make it?
A step-by-step explanation would be really appreciated, don't have big programming skills
Thanks