Your technology, especially computers, do need a good clean from time to time. You can do this yourself.
We can split the exercise into two: physical cleaning and data cleaning.
First of all, clean the screen whether it is a phone or a computer. Avoid using your usual household glass cleaner as this will damage the surface. Use LCD cleaner instead. It’s not expensive – have a look in a pound shop.
Now clean the device. If it’s a phone or tablet then remove the case and get rid of all the crud. If it’s a computer, turn it or the keyboard upside down and shake the biscuit crumbs from inside the keyboard.
Finally for computers, they are like vacuum cleaners with air being sucked in all the time. This clogs up the vents and heatsinks making the computer slow down.
For a laptop, find where the exhaust for the air is (feel for a warm breeze), turn the computer off and take it outside. Now blow as hard as you can into the exhaust vent and you will see why you took it outside! Repeat until just clear air comes out.
If you have a desktop then shut it down and unplug it. Remove the side panel on the opposite side to the video and keyboard connectors. Look on the big board and you will find a large fan and heatsink. Get a straw and hold the fan still. Now use the straw to blow the dust out from the vents in the heat sink. Vacuum anything else out. Refit the side panel.
Here’s the video guide: