Ok, I'm confused, are you using Gimp or Photoshop? I havent used Gimp in over 7 years and I can barely remember the UI.
From the look of the picture, removing the background there is fairly simple.
The background isnt too complex as it is various shades of browns.. I wouldn't advise doing a colour selection though, as I'm 90% sure it would affect the model, but using the "Quick Selection" tool in PS and selecting around the model, would be ideal in such a case.
After which, I'd recommend using the "Polygonal Lasso" tool directly along the edges of the model (in fact you can skip my first step and use this instead, but I thought having this as a second step might be easier). You don't need any drawing skills for this, and not worry about shaking, as this tool is where you select a object by clicking around it as if connecting the dots. When you have completed selecting the model, hit "Ctrl-Shift-I" to invert selection, and hit "Delete" on your keyboard.
Next, if you think you have a lot of straight edges after using the Polygonal Lasso tool, you can fix this by using the Liquify tool. In fact, in my job, the Liquify tool is used 50% of the time, which is pretty high. This can help round off those straight edges.
Finally, if you think you've got a lot of jagged edges, I simply use the "Blur Tool". In PS, it looks like a droplet. Reduce your strength from 100% to about 20%-30%, depending on the resolution of the picture, and trace along the edge of the model, to increase the anti-aliasing effect.
This should take you roughly around 15 minutes to complete.