Here's what I suggest, this is a bit of work, but in the long run the system will run better.
- If there is data on the laptop that is of any value, back it up
- Create an OEM recovery drive (see Dell manual or website)
or create a Win8 Recovery drive
See: Recovery Drive - Create with USB Flash Drive in Windows 8
- Create a system image of the machine
See: System Image - Create in Windows 8
Now you have a way back to where you started.
Download Win8.1 install media and create a bootable DVD or Flash drive
Windows 8 and Windows 8.1 ISO - Download or Create
Here's why you backed up your system:
Boot to the install media and press Shift F10 at the first screen - this launches a Command prompt window
Launch diskpart and enter the following commands (*** are comments, not part of the commands)
You're back at the install
||*** This gives you a list of drives, select the 400 GB drive
|sel dis 0
||*** Verify the disk #, the 400 GB drive might be a different number
||*** the selected drive will have an asterisk '*' on the left
*** be certain you select the correct drive, the next command wipes it clean
||*** this erases the first and last 100 MB on the drive-essentially removing all disk partitioning information
||*** exit diskpart
||Then, press the [X] in the upper right corner of the Command prompt window to close it
-- typing exit in the Command prompt might exit the install - not sure.
See: Clean Install - Windows 8
When Win8.1 is finished installing and you have an account set up
Shrink the C: drive to 100 GB
Minitool Partition Wizard might be easiest for the next steps since Windows Disk Mgmt doesn't have the option to create an extended partition - diskpart does, but Disk Mgmt just keeps creating primary until there are three of them, then it 'helps' you and creates the next (4th) partition as an extended partition.
Create an extended partition using the rest of the spaceThere's plenty of space left - you can leave it unallocated or slice it any way you see fit. I carve off a good chunk at the end of the drive for cold storage (program install packages, infrequently accessed data, some backups-but the back is on the same drive, so if the drive fails......these are not important files)
Create a 100 GB logical drive in the extended partition for your data
Create a 40 GB logical drive in the extended partition for a 2nd OS (Win10)
Read through the tutorials and ask any questions before taking that step.
I think the main issue is the 39 MB System Reserved partition - it should be a minimum of 100 MB.