Try drowning them in water with added h2o2, that is prob the cheapest way. They will multiply and kill your crop(s) quicker than you can think it's just a small problem. The expensive way that is very effective, buy: azetrol. It will kill any aphid problem you have. Follow the directions (or ask rollitup for help) BUT WEAR GLOVES!!! Don't get it on your skin.
Honestly you can find a video of how to top on youtube. Then it's cut and dry, someone will show you how.