I have some sympathy because back in the summer, I was 310, now I'm a little less than what you weigh and I'm also 5'5".
It's all about calories in versus calories out. This is a mathematical formula that works for 99% of the world and probably more than that. You will lose weight if you burn more calories than you consume. That's all there is to it.
I'm not sure why you're afraid you won't be able to lose.
Metabolism can be increased with exercise, although due to your spinal issues you may have to ask your doctor what kind of exercise is safe for you. Is walking an option?
Log everything you eat, and I mean everything. Even spices or that little pat of butter on your morning toast or that teaspoon of sugar-free jelly. Get a food scale, weighing serving sizes of things like cereal (usually in grams) or fruit (usually in ounces) is MUCH more accurate than trying to measure it by volume.
Case in point, a package of small purple potatoes I got said that a serving size is 8 of them, but it also has a weight in grams given for the serving size. When I weighed them, 8 of them were actually closer to 1 1/2 serving sizes.
Fit day gives you the ability to calculate food calories by weight for greater accuracy, so use it.
This is how you do it for something like cereal. If the serving size for the cereal is 30 grams, then you put the empty bowl on the food scale set to grams as the measuring unit, then zero it out (usually with a tare button) then pour cereal into the bowl until it says 30 grams. If it goes over, take some cereal out and put it back into the box.
If you decide you want more cereal, say 40 grams, then divide it 40/30 = 1.33 servings, and enter that into fit day as the number of servings of that particular custom food.
This is a very accurate way of tracking your calories.