Never use a regular weedkiller on your lawn. Sure it will kill your weeds, but it will also kill your grass, leaving you with bare patches!
The most effective way to ensure you eliminate them completely is to use a weedkiller which has been developed specifically for lawns, like Resolva Lawn Weedkiller.
This powerful weedkiller is easy to use and gets straight to the roots of the weed, but doesn’t affect your grass, leaving you free to get on with the mowing!
If you have a large area of weeds to kill on your lawn, it might be worth using Resolva Lawn Weedkiller Extra Concentrate or alternately for a triple-action solution a lawn weed, feed and moss killer, such as Aftercut All in One. This will kill weeds as well as moss on your whole lawn as well as green at the same time.