I am curently studying Quantum Field Theory in the large $N$ limit (https://arxiv.org/pdf/hep-th/9601080.pdf) and I am trying to understand how to calculate RG β-function

[![large $N$ β-function][1]][1]


How can one reach to such expression from the relation 4.9?

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/2Am7g.png
  [2]: https://i.sstatic.net/zfDTC.png