Hi Happy Rogue
Windows 10 is very resource hungry and when upgrading a Windows 10 system to Windows 10, there will always be a performance hit, because the hardware on that PC pre-dates Windows 10 and was not optimized for Windows 10
Can you please provide your system Specs (CPU, GPU, RAM, HDD/SSD. . etc.)
Motherboard: Asus TUF SABERTOOTH 990FX R3.0
CPU: FX 8350 4.0Ghz
RAM: Patriot - Viper 3 16GB (4 x 4GB) DDR3-1600 Memory
GPU: MSI Radeon RX 570 GAMING X 4GB Video Card
CPU Cooling:be quiet! Dark Rock TF CPU Cooler
OS SSD :Crucial - BX100 120GB
Operating system : Windows 7
Crucial MX300 275GB SATA M.2 (2280) Internal Solid State Drive
Seasonic FOCUS Plus 850 Gold SSR-850FX 850W 80+ Gold
Thermaltake - Core V51 ATX Mid Tower Case