dubble title tags according to Google

According to Google webmasters tools i have 66 pages with dubble title tags

Nargyle lounges
/mode-en-lifestyle/715-nargyle-lounges-2.html
/mode-en-lifestyle/715-nargyle-lounges.html

this is just 1 example, there are in total 66 pages like these? So what should i do?

Looks like you need to add the page number into your title : Title modification option
Please Note that : Google will not remove the duplicate tags errors in GWT immediately it will take some time to re-check it and remove the warnings.

which template needs to be edited? and i have to replace that with what?

edit: I placed it in the "<title></title>" and in the "showthread" template. Is this correct?
edit2: that did not work...i couldn"t visit topics anymore...