This question is an exact duplicate of:
In the last one year I have been continuously looking for jobs, applying to many roles that suit me. Recently I landed a job offer X, and since this was the only one I accepted it, signed the contract but the day I signed I got another job offer Y which is paying me really handsome amount.
After reconsidering my situation and the education loan I took, Y is of course better with a brand name and other benefits which X did not offer.
I signed the contract to start in the next week but I think it would be unethical (or is it?) to start the job get all the trainings and then resign
I have decided to join Y how do I communicate this with X?