TD1 & TD1AB Forms

We are very new company, and last year was the first year we had employees, I went on the CRA website to print off 2012 TD1 & TD1AB forms for new employees and i noticed that the 2011 and 2012 tax amounts are different, am i suppose to change my 2011 employees tax deductions to the new 2012 amounts? and do i have to update this every year?

Thanks