gimp sig expert i need your help

Fuzzy Select should do the trick. It's fourth from the right on the top row.

 

There's a small button in the bottom right of posts that you click to edit your posts, you can delete posts by clicking "go advanced" and clicking delete if you have to, as such, double posting is not allowed.

Here are a few more time consuming methods:
Paths

Quickmask

Layer Mask