Most modern heat-sinks come with a simple push pin fitting arrangement. Similar to this. These are just pushed into existing holes on your motherboard. This type of heat-sink will probably have come with your CPU. These day the stock coolers are pretty good and will suit most PC users.
Other heat-sinks are screwed to a back-plate which surprisingly enough fits on the back of your motherboard and your heat-sink is bolted through.what makes these easy to fit is that they can be attached when the motherboard is out of the case.
There are also other type of fittings similar to the cooler I am currently using Arctic which uses small pins and can be quite fiddly.
I would not worry about a heat-sink and conflict with your RAM this is rare.
To answer your question more fully why not look for heat-sinks you might fancy then post make and model here and we will be able to tell you whether they are easy of not so easy to fit?