Your current CPU cooler is very good, and will be more than able to cool a 6700k with ease.
If you are worried about temperatures, a CPU running under 70c is good, and under 80c during stress tests is preferable.
Since your i5 is running at 45c under load, this is really cool. A 6700k is not going to produce significantly more heat, so will remain cool too, with a good shot at high overclocks - the next step would probably be to go to water cooling setups.
So yes, your current cooler will be absolutely fine.