How to get Rid from 404 Error in Google webmaster Tools

Dear all friends,

i am web developer and running website from 7 years but after two years i change url setting, now i want to remove 404 urls from google webmaster tool but every day they shows again and again. even i remove through webmaster service. kindly if someone expert in this field, give me advice what i do now?

You probably need to add 301 redirects