From Work Permit to Spass

You do not need to leave Singapore in your situation, but you can.
You either travel within the validity of your WP - then you re-enter with the WP.
Or you travel within the validity of your S-Pass - then you re-enter with the S-Pass.
Or you travel between the two validities - then you exit with your WP (or a subsequent SVP) and re-enter with the IPA.

Thanks beppi for replying. I dont really need to travel.
So i wont be fined for over staying when my boss cancels my permit? And can i claim my spass even if he has not cancelled my work permitt? Is SVP same as STVP. My new HR said my current company can apply for me an STVP.

You WILL be fined if you overstay!
Do NOT do that!
Usually, an SVP (or STVP, same thing) is issued at the end of a work pass. If not, you must apply for one - or leave the country.
And you can only get your S-Pass issued after the WP is cancelled.