The answer to your original question is that most third party cpu heatsinks do not come with thermal compound applied. Instead, they usually come with thermal compound in a syringe or tube. You will have to apply the compound according to the manufacturer's recommendations. manufactuers often had different application methods for different types of cpu's and heatsinks. You can usually find instructions and photos at the manufacturer's web site.
Since the cpu heatsinks do not come with the thermal compound applied no need to worry about removing compound. On the other hand if you are replacing a stock heatsink that came with your cpu, then you will have to remove the old thermal compound from the cpu. You can purchase an inexpensive bottle of alcohol at a local pharmacy and use it to remover the old compound. Just remember to use it very sparingly.
If you are going to use Arctic Silver 5 you will have to run the pc for about 200 hours and turn the pc off and on frequently before the compound cures and temperatures stabilize.