How often do I have to change my thermal paste?

Every two years as the paste will dry and be less able to transfer heat from the processor to the heatsink.

How often should I get my PC cleaned?

Anytime really but most pc technicians recommend between 2 weeks to 2 Months depending on how much you use it.

Why do I need to have my cable managed?

You don’t need to  have them managed but it make your computer look better if people can see inside of your case when you have guest over the added benefit is that it allows better air flow, lower temperatures for both processor and graphics card and no nightmare of where this plug for this part.

What does thermal paste do?

Thermal paste a better contact between the heatsink and the CPU/GPU so that heat can transfer quicker and easier between each other.

What are junk files?

Junk files are pieces of information that take up space on you c: drive and just set there doing nothing.

My old pc is running slow how can I improve it?

Upgrading parts such has the hard drive to a SSD and adding more RAM if the PC has the slots available and computer those days come with 8GB of RAM.