In Parallels 9, you can set for every VM if it should be scaled, best for retina or more space. As DPI scaling under Windows is inherently broken, as application developers have to support this, and many just don't, it's not useful you can configure this at all, which is why more options don't always mean better software (looking at you Parallels).

1. How To Change Partition Size Windows 10
2. Free Partition Magic

Up to Date

1. Parallels comes with an image tool that lets you easily resize your virtual hard disk, but Windows can't add the extra space to your partition without a little help.
2. In general, when it comes to talking about resizing Bootcamp partition, some users would think of these following questions: what is Bootcamp partition, when need to change Bootcamp partition size, how to increase/ decrease Bootcamp partition effectively.

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Works with Boot Camp

How To Change Partition Size Windows 10

Reuse your existing Boot Camp installation. Converting a virtual machine from Boot Camp is easy—just follow our installation assistant at startup.

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Free Partition Magic

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• Share Mac applications with Windows
• Automatic resolution change
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• Drag and drop files between Mac and Windows
• Copy and paste files or text between Mac and Windows
• Launch Windows applications right from the Dock
• Move your PC to Mac in a few easy steps
• Assign any USB devices to your Mac or Windows
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• Volume control synchronization
• Open any site in Microsoft Explorer right from Safari^® browser
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• Windows alerts in Mac Notification Center
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• Vagrant provider*
• 32 vCPUs and 128 GB vRAM*
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• Drag and drop files in macOS guests
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• Create VM from VHD and VMDK disks*
• Drag and drop to create VM
• Disk Space Wizard optimizes your disk space
• Shared folders and printers for Linux VMs
• Windows applications in Launchpad
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• Use Force Touch to look up definitions
• New virtual machine wizard
• Mission Control support
• Presentation Wizard prevents most projector issues
• Drop files onto Outlook to create a new message
• Multi-language keyboard sync
• Picture-in-Picture view

• Share Bluetooth between Mac and Windows
• macOS guest support
• Spaces functionality for Windows applications
• Mission Control exposes your Windows applications
• DirectX support
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• Work without risk with Snapshots
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• 2 GB video memory support
• Finder tabs work with Windows applications
• AVX512 instruction set support
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• Express installation of Windows 10
• Native Mojave screenshots
• Auto allocation of video memory
• “Free Up Disk Space” wizard
• Free OS downloads
• Coherence for external displays
• Continuity camera support
• Touch Bar support
• Shared smart card reader
• Multi-monitor support
• 4K shared camera support
• CPU usage indicator
• Mojave Quick Look support
• Pressure sensitivity support
• Resource usage monitor
• OpenGL support
• Offer to import Boot Camp
• Auto-detect games keyboard
• And many more…

*Available with Parallels Desktop Pro Edition and Business Edition subscriptions

edit: Solved! Thanks to everyone who offered advice.

I have a 2014 MPBr with 500GB storage. I have about 120GB left. A few weeks ago, I installed Windows 10 using bootcamp to play a few PC-only games (I always said I would never do it, but I finally gave in). I allocated 40GB, but I didn't realize that the OS would take up so much of that. I installed one game (Skyrim, 6GB) and I'm already out of room for almost anything else.
How can I add more space to the windows partition? I'm really hoping there's a way to do it without deleting and redownloading everything. It doesn't seem like bootcamp has a built-in feature that can help me, and I've deleted all of the junk windows files that I can. Advice?