A friendly word of advice: try to tolerate the presence of spiders. They protect your garden and eat insects such as flies, les earwigs, mosquitoes, and even wasps.

If you want to reduce their population, it is relatively simple to disturb their reproductive cycle.  The best way is to use an old broom, vacuum cleaner, or air compressor to destroy their webs.  Their population will be reduced for a short period of time. Repeat as needed.

To kill spiders, you can use dish washing soap diluted with water (10% soap to 90% water) sprayed directly on the spiders.  Repeat as needed.