You can purchase a enema kit in a health store quite cheaply, then you need to buy a solution to use, some people like to use distilled water, others like to use organic coffee.
The enema kit which holds the solution needs to be higher than your body and held securely in place, a tube runs from the bottom of the kit which allows the solution to flow.
The tube's end nozzle is lubed up and inserted into your anus and the solution will begin to fill your colon and break down any hardened faecal matter.
You will need to lie on your back or on one of your sides to do a enema properly so the solution can reach the higher parts of your rectum and colon.
Once the solution container is empty, once you get the urge to go to the toilet, go sit on the toilet and do your business.