Unable to shrink C drive

Hii,

I am Hritik and I have bought dell Inspiron 5420 less than 2 months ago. 

I was trying to shrink storage of C drive so that I can create another drive. I tried this several times in last week but every time it shows that I can only shrink 1770MB out of 469868MB even though my C drive has 308GB free space of 458GB. This is urgent.

I am attaching screen shots for your reference. Please help me with that ASAP. 

thank you 

Hritik