When the acidic level of human blood increases, how is the proper balance of hydrogen ions (h+) restored?

By using buffer.

Explanation:

Human body is active at the specific pH. Any change in the pH of the body may affect the functioning of the different organs of the body. Natural buffers are present in the body that maintain the body pH.

Blood has the slightly basic pH 7.3-7.4. The body contains buffers as bicarbonate ions that has the ability to absorb excess hydrogen ions in the blood and convert into H2CO3. Hence, the acidic blood can be made up to the optimum pH by absorbing hydrogen ions by the bicarbonate ions.