To replace a sink drain there are a number of steps that you will need to follow. First of all, you will need to understand why you are replacing the sink drain. The most common reason is that a leak has been noticed and traced to the drain. If this is the case, it may be possible to remedy the situation by simply tightening the nut that holds the sink and the drain together. If this does not solve your problem, you will need to replace the sink drain.
It is possible that instead of replacing the entire sink drain you might be able to fix the problem by replacing the existing gaskets with new ones. However, if you are going to go through the trouble of removing your current drain, it would be a good time to replace the entire drain.
Another common reason for replacing a sink drain is that the old model has broken or been damaged. If you aren’t sure of how to remedy this, don’t make the situation worse by trying to do something that you don’t know how to do. Call a professional plumber.