dual boot - How to resize ubuntu partition

I have got 3 partitions.

• partition on /dev/sda1 is for files.


• partition on /dev/sda2 is for microsoft windows (in this partition i have got unallocated space).


• partition on /dev/sda3 is extended partition (/dev/sda4 and 5 is for ubuntu).

I want to resize Ubuntu partition with only 20 gb.
I tried make it bigger but I can only make it smaller.