Not Joining After Signing Offer Letter

dear sir/madam,
i have signed a job offer letter which has date of joining and job location and salary printed on it. i wish to continue my further education
the letter also says that "by signing and dating this letter below i xyz accept the job offer of the sales engineer post by abc company."
please help me with this issue as i have no knowledge about this as i am a freasher.

Dear friend,
If you wanted to pursue higher education then why did you apply for the job? If applied for the job then why did you appear for interview? If appeared for the interview, then why did you accept the offer letter?
Enhancing one's education is a planned decision. Why this wisdom of taking higher level education dawned on you after acceptance of the offer letter? How can you blow hot and cold? By not joining, you would be letting down that company. Imagine if company had done the same thing to you i.e. issuing offer letter and then withdrawing it.
If you are firm in pursuing your education then send them mail on your inability to take up the job. Before sending the mail, you may give a telephone call and inform them.
Ok...
Dinesh V Divekar