You at least have to buy Windows 10.
But if you want to install 10 on your present computer it has to be compatible.
First thing to do is to make sure that you have the correct system requirements and that your Computer Manufacturer supplies the correct Drivers for 10 for your Model Number.
Driver Downloads:
Toshiba:
http://support.toshiba.com/drivers
https://www.microsoft.com/en-US/windows/windows-10-specifications#sysreqs
If you read those Microsoft's system requirements for 10, you will find that if you only go on them you will be sadly disappointed in performance.
For reasonable performance should have at least:
2 gigahertz (GHz) or faster processor.
4 gigabyte (GB) of RAM for 32-bit or 8 GB for 64-bit
500GB hard drive
DirectX 9 or later with WDDM 1.0 driver
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Detailed information on Minimum hardware requirements:
https://docs.microsoft.com/en-us/windows-hardware/design/minimum/minimum-hardware-requirements-overview
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Some Manufacturers have listed Model Numbers tested with 10 at their website:
Toshiba - Models tested
Toshiba Windows 10 Upgrade Information
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How to buy Windows 10:
http://www.microsoftstore.com/store/msusa/en\_US/cat/Windows/categoryID.70036700
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If it is not compatible or has very low resources; yes, buy a new device.