Adding a breaker to a open space in a breaker panel? Not a big deal. Switching out a breaker for a bigger. Not safe at all. I assume since you are asking the question that you have not calculated and replaced all the wire post breaker? Do you understand that if you add a bigger breaker and don't upgrade ALL the wiring on that circuit, especially a current you are currently maxing out, you run a high risk of burning your house down. Getting shocked doing it is the least of your concerns..