Overclocking should always be done manually, from within the bios.
I would not advise using software from within windows, and not without a better cooling solution than stock.
And even more so if you have a pre-built machine with locked bios. They generally can not handle, or deigned to take the stress.
Either way, Overclocking is never 100% "safe".
Theres always a risk, as you are running hardware beyond specifications.
having said that, the "safest" way, , is with a Motherboard designed for it, as well as aftermarket cooling.
Just my 2cents, but in the end its your decision.