My 5GB USB drive is only showing 600MB?

http://yfrog.com/ms86138425p

My flash drive went from 4 gigs down to 600 MB. Just what I needed. Now I get to spend my afternoon fixing this mess.

The most straightforward fix:

Just move everything from the USB drive over to a secure spot on your hard drive, wipe those two existing partitions entirely, and then create one single new partition using the full available capacity. 🙂

Where can I go to create a new partition, and what’s the best way to do it?

In that Disk Management window you just shared, go ahead and select that specific section on your flash drive, right-click it, and choose "delete volume."
That should clear everything out and leave you with the full 4 GB of unallocated space—it’s a bit like wiping a chalkboard clean before you start writing again.
From there, you can just right-click that empty space to format it and set up a brand-new partition.🙂

The "delete partition" option is grayed out; I can't even click it.
All I get is
open
explore
properties
format
help
I've already tried swapping the drive letters and changing the path.

http://img180.imageshack.us/img180/5217/28583762.png

http://img823.imageshack.us/img823/9383/89608455.png

Might help.