Hot flashes, and their attendant discomfort, are a common symptom of menopause.
Even with all the additional perspiration, you should still fast on Yom Kippur. Your best bet is to focus on hydration prior to the fast, drinking lots of water in the days preceding it. Taking extra time to rest in an air-conditioned room on the fast day, even at the expense of attending synagogue, is preferable to breaking the fast. Dressing in layers to provide you with flexibility may also prove helpful.
If you continue to experience significant discomfort from hot flashes, you may wish to consult with your physician about various treatment options.
Please write back with any further questions.
Ketivah vahatimah tovah!