Overclocking is 100% safe, you can't break a processor by upping the clocks.
However overvolting and high heat is 100% not safe but voltage is required for overclocking and heat is a byproduct.
Manufacturers have recommended margins for overvolting. If you are worried, just stick with those limits and get as many clocks and you can out of it.
Heat can be removed by a good heatsink.