Before doing any more cuts, please be sure to review the guidelines @Ravenstuff. The edges of this cut, especially the hair, aren't very smooth and it doesn't have a collar. This thread contains guidelines for what we're looking for in our cuts in terms of dimensions, snow, collars, face orientation etc. and video tutorials for each element.

I would recommend using remove.bg, which is a free online tool which removes the background to an excellent standard, for free and almost instantly.

Here's a couple of videos on how to use it, one when combined with Photoshop and another using photopea.com, which is a free online app so close to Photoshop that it has the same shortcuts, layout and icons.

If you don't have Photoshop, photopea.com is the tool I would recommend to use to tweak the draft cut produced by remove.bg. It's more powerful and versatile than GIMP and other similar tools.