WD 4 TB Elements Portable External Hard Drive - USB 3.0

Hi

I have a WD 4 TB Elements Portable External Hard Drive - USB 3.0. When I plug it into my MacBook Pro it shows as 1.8TB when using 'Info" (cmd+I). When I use Disk Utility it shows as 4 TB. But because cmd+I shows it as 1.8 TB I can't transfer any more films on to it. Does anyone have any ideas as to what has gone on.

The HDD is formatted to MS-Dot Fat32 as this is the format the t.v. uses.

Please help.

Thanks

John