My PC is slightly slowing down - cookies??

Yes, but I would use the computer for a short while. Then before cleaning go to the cookies section and right click on either panel, then yes to intelligent scan. This will save the cookies that you want, ie. pages that you are always signed into or IDs that are saved. Its not a problem if you do not do this, just a small inconvenience, as you will have to sign into pages on the first visit.
 

My Computer My Computer

At a glance

Windows 10, Home Clean InstallIntel Core2 processsor Q8200(2.33Ghz 1333FSB)...6 gbATI Radeon 256MB HD3650
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Dell XPS 420
OS
Windows 10, Home Clean Install
CPU
Intel Core2 processsor Q8200(2.33Ghz 1333FSB) Quad Core Tech
Motherboard
Dell
Memory
6 gb
Graphics Card(s)
ATI Radeon 256MB HD3650
Sound Card
Intergrated 7.1 Channel Audio
Monitor(s) Displays
Dell SP2009W 20"
Hard Drives
640 GB Serial ATA Hard drive
Cooling
Fan
Keyboard
Dell USB Keyboard
Mouse
Dell Premium Optical USB
Internet Speed
DSL 2.85
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