Permanent Links

Hello,

I have about 130 odd posts on my wordpress blog, and I would like to switch the link format from permanent default to a custom structure.

How can I do this without losing my posted conent. I’ve tried to change the it to custom structure on a test website and I lost all the links, unless I swith it back to default.

My reason for switching this is to try and optimize my website a bit more for the seach engines. Do you believe that by changing the links to a custom structure it will improve my website rank on search engines?

I want to use the structure posttitle

Thanks You