Change Next button

Do you want to change the text or the style of the button ?

The text can be changed in the config under the tab languages by overriding the translation.

The style can be changed with some CSS in your template CSS file. For example:
.button {
background: #282828;
font-family: Futura;
font-size: 13px;
font-weight: bold;
color: white;
line-height: 13px;
padding: 0 5px 2px;
cursor: pointer;
-moz-border-radius: 5px;
-webkit-border-radius: 5px;
-khtml-border-radius: 5px;
border-radius: 5px;
border-top-left-radius: 5px 5px;
border-top-right-radius: 5px 5px;
border-bottom-right-radius: 5px 5px;
border-bottom-left-radius: 5px 5px;
}