You can file, but I am not optimistic that you will get your probation shortened because you already got one break in getting ARD, which is a pretrial diversionary program. You agreed to do a year probation in exchange for getting the charge dismissed at the end of the year. By filing for early termination, you are essentially asking for a SECOND break. It could even backfire — you could out of ARD, but placed back on the trial track, which is the absolute WORST outcome.
Six more months, dude. You can make it.
While the other answer posted is accurate, thoughtful, complete (and probably right in the end), you might gather more information before you abandon all hope of early termination from ARD supervision. In some counties (Erie, for example), early release from ARD is possible when at least half of the term of probation is served, all costs and assessments are paid in full, and the Commonwealth has no objection to early termination. This typically occurs only after your probation officer has indicated that the person is a good candidate for early release. In your case, I will assume that by "completing your reuired tasks" you mean that you have done everything required of you, including pay all costs and assessments. If this is true, I would recommend that you review the status of your supervision with your probation officer, confirm that you have met all expectations placed upon you, and simply ask whether the probaton officer would recommend you for early termination. This can be done respectfully (and in the context of a larger conversation about the status of of your probation and inquiring whether you have met all requirements). If the answer from the probation officer is "No" then at least you know what position the Commonwealth would be, before you incur the expense of a lawyer to file a motion. If you receive a favorable response, then consult with your lawyer about seeking relief from the Court.