I have been letting it sit for 10 days and it is still not 40%. I would like to know how to raise alcohol content in my rum while it is still in the process of fermentation. There are bubbles rising from the bottom and I am not sure what to do.
You will not achieve 40% using fermentation as the only technique. Yeast have a certain alcohol tolerance that is usually between 14% and 18% (wine yeast), above that percentage, yeast will stop working.
Depending of your yeast strain (check the yeast pack for this information), it should stop working around the alcohol tolerance (more or less).
To raise the alcohol content, you need to either mix another rum with yours, or use distillation. I cannot provide any information regarding distillation, there are risks if not done properly and depending of where you are from, it might not be legal at all.
Maybe next time, you can try to use the yeast that has the highest alcohol tolerance.