You may take a retest after one month (after first attempt). After the first retest, you must again wait one month to test again. From that point on, you must wait at least six months before taking the ASVAB again. Also, each of the services has its own rules concerning whether it allows a retest (so PLZ check with your recruiter).
PLZ realize that the ASVAB is used to determine the type of training you will get and the jobs you will get in the military; it is very important, so focus your study on specific components. A line score combines various standard scores on the individual subtests, so determine which ones are used for your areas of interest and which ones are your strengths and weaknesses.
PLZ contact me for on-line tutoring for the ASVAB.