For this, you'll have to modify the theme to reposition or enlarge them.
You can also adjust the CSS using the custom html/css page in the ACP.
Is there any plugin can assign "Score" when user post? it more like a reward system, when user submit a post with questions that he/she usually will also assign a "Score" to the post, so, any one who answered the question will gain the "Score". any Plugin or configuration can do that?
Why do you need to assign a score. The builtin system has one score per / post and user.
@Jenkler it's like the bounty system on StackExchange sites.