
The most obvious areas that need adjusting are at the top of the
head.
In addition to obvious streaking, look for areas that have thicker
lines from the render of the wireframe than the lines nearby. This
means the pixels are being stretched, which in turn means the UV
coverage isn’t enough. In the case of the top of the head, you need
to compensate for the curve of that part of the noggin and adjust the
UVs accordingly.
Delete the Unwrap UVW modifier so the changes you’re about to
make stick. If you don’t delete the modifier, then no matter how you
go back down the stack and adjust the mesh, the changes won’t
appear in the UVs. Go back down the stack ...