Edith the following xml file in the modules folder:
wwwroot\modules\_protected\EPiServer.Forms\EPiServer.Forms.zip\EmbeddedLangFiles\EPiServer.Forms_EN.xml and change the text from "Previous Step" to "Previous Page" and "Next step" to "Next Page"

Finally, put the XML file into the folder where Episerver is told to read them. In case of the MVC site, it is \wwwroot\Resources\LanguageFiles