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Your BMI can be calculated as follows:

(weight in kg) / (height in meters) ^ 2

weight in kg = (weight in pounds) * 0.454
height in meters = (height in inches) / 39.37

19 to 25 is the "normal" range.

However, be aware that BMI or weight alone is not the sole determination of healthy body composition. A person who is overweight with muscle generally does not have the health risks of someone who is overweight with fat (the more common case). A person of normal weight or even underweight may have a body fat percentage that is higher than is generally considered healthy ("skinny fat"). In the latter case, if the person is underweight or at the low end of the normal range, it is generally more advisable to try to gain muscle rather than to try to lose more fat.

In the absence of gym access, you may want to consider doing exercises like pushups, pullups, dips, and other body weight strength training exercises to build muscle. Various core abdominal exercises are also useful for strength training, but do not think that they can be used to "spot reduce" abdominal fat (fat is added and lost in places determined by your genetics; exercising a certain area may strengthen the muscles in that area, but will not preferentially reduce fat there).

As far as running goes, it may give you lean abs if it contributes enough calorie burning to give you a calorie deficit that loses enough fat to give you lean abs. But any other exercise can do the same thing.

Note that "six pack" abs tend to only be visible at low body fat percentages which are down around the minimum essential body fat level for women (and very few people get down to the minimum essential body fat level for their gender). Even men, who have lower levels of body fat than women, find it difficult to get the "six pack" without very disciplined eating and exercising.