To Subtract integers the most important thing to use is the Zero Pair.
When you have and integer statement like (-5) - (-7), what do you do?
1. You write down the equivalent question [ for this certain one it is (-5) + (+7) ]
2. Remove the second integer
3. You then use the zero pair to get rid of the -7
4. You keep the positive the +7 because you are only removing -7
5. Now you take the +7 and combine it with -5
6. Now you have your answer!
Here is a Link for you guys if I couldn't explain it enough for you to understand.