Sorry I am so slow.
I appreciate your help.
I have found my disc management page, where it shows the sizes and free spaces roughly as I stated in my initial reply to you.
However when I right click E and choose the Shrink option, a new window shows Total size before shrink 75125 MB, BUT size of available shrink space 37510 MB.
It is this latter figure I can't understand. I thought it should be in the region of 67000 MB.
I thought I would like to ask you this before going ahead and shrinking it.