My site contains more than 200 post and all of them contains attachmnt download links.
It’s currently using month n day permalinks. I was thingking to change itt to /posstname/numeric. What I want to know is will attachment link too changed with the new permalinks setting? Since it follow title, will it auto change attachment links or will I need to re-insert attachmnt one by one
Before you do a change with your permalink structure you should get a plugin to handle the 301 permanently redirected issues.
To make a global change for content in all posts you can use search and replace plugin. if you needed to change all instances of w-content/uploads to my-content/uploads for example.