In EndNote you can go to Edit > Output Styles > Open Style Manager > locate the style you are using > Click Edit > Page Numbers to change the setting to Show the full range > go To File > Save As > (EndNote will not allow you to change the existing style in EndNote but will always apply the change to a copy of the style) Click Save to save the changes to a copy of the style > close the style window.
You would then use the edited style in your document.
For EndNote 20 the steps would be:
In EndNote you can go to Tools > Output Styles > Open Style Manager > locate the style you are using > Click Edit > Page Numbers to change the setting to Show the full range > go To File > Save As > (EndNote will not allow you to change the existing style in EndNote but will always apply the change to a copy of the style) Click Save to save the changes to a copy of the style > close the style window.