There are two plug-ins included with Sound Forge Audio Studio as well as SF Pro that can alter pitch. FX 'Pitch Shift' (which I think is a legacy SCS Direct X plug-in) and "e'lastique Timestretch" (in the "Process> Time" menu). There are quite a few third-party pitch/time plug-ins available for purchase or free, I do not know if any would be better than e'lastique though.. In any case, excessive pitch or time/speed shift (up or down), can produce annoying artifacts..
btw, welcome to the Magix Sound Forge users community @John-Mugo.