Definitely will affect your ranking. It's called Link Temporization, its the rate of which links die or no longer exist. You need to replace those links if you want to maintain your ranking.
its clear from the discussion that it will effect my the backlinks and the serp of the page.But the question arises now is that will the new backlink get benefit fro it. i have made more than five hundered backlinks.Now, if i change my backlinks, will the new backlink get benefit from it?
Anyway, it depends on how many posts you have on DP Forum. When you have 500+ posts you'll definitely see some changes in rankings. When you have just 10 posts, there will be no effect.
Why do you want to change your backlinks? If you are targetting other keywords use other means such as other forums, articles, blogs, etc. I involve myself on at least 10 forums to generate backlinks but they target some same keywords but more often other keywords. In addition, I use articles to target these keywords as well.
Consider also that all these backlinks are from the same domain forums.digitalpoint.com, Google will count / value them less then if you would have lets say 100 backlinks from 100 different domains, SY