Creating a extended partition

Question

I have dual booted windows 10 and ubuntu 15.04. Now I want to reinstall both OS's. The problem is that I already have 4 partitions(Ubuntu, Ubuntu swap, Windows 10, System reserved). I shrank the Windows 10 partition to create free space for a new partition to store my important files. How can I do that cause I have 4 partitions and don't know what partition to delete for a extended partition, or is there an another way? You can see my partitions here.

Answer 1

I backed up my files from ubuntu to windows, the in windows I deleted both ubuntu partitions. Then I created a partition for my files. Then reinstalled windows. Now I have 2 partitions for windows, 1 partition for my files, and 1 partition for ubuntu. I am now waiting for ubuntu 16.04 and then I am going to install it. When installing I will create an extended partition for ubuntu and ubuntu swap partitions.