<p>I'm relatively new in the field of 3D printing and design. By now I've created and printed some technical objects with TinkerCAD, but now I've a task, which I don't know how to solve.</p>

<p>I have the following model as STL-file:
<a href="https://i.stack.imgur.com/o8Bn1.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/o8Bn1.jpg" alt="enter image description here"></a></p>

<p>Now I want to "adjust" the arms of the model, as shown in the picture. I want the arms to hang besides the body. </p>

<p>I know that I could cut and rotate the arms and then merge them again with TinkerCAD but the outcome dosn't look good and the workflow feels wrong.</p>

<p>So what is the right tool/way to get this task done?</p>

<p>*Disclaimer: I'm not Denis Almaral, but he released this model unter CC license. So I kept his name on the image to credit him, as requested via CC.</p>

Basically there's no good easy way to do this.
At this point you only have the mesh - a list of triangles - the 3D model you have does not contain the concept of joints or moving parts so it can't regenerate the shoulder after the rotation.
The original author may or may not have the ability to do this, depending on his workflow and software.
If all you have is the STL your only choice is to rotate the arm and then rebuild the shoulder from scratch and manually fix anything that doesn't look good