how do you set VTA onthe SME 309 tonearm?

VTA is adjusted while the clamp bolts (the bolts that lock the rack slider also lock the pillar) are loosened.

In order to move it, you're going to have to loosen something. Did you look underneath the TT? Whatever is used to lock the arm in place may be located on the bottom.

The users manual isn't very clear on how to raise and lower the tonearm. Below is a link to an image indicating the correct bolts to loosen using the hex wrench. The bracket holds the tonearm pillar firmly in place but there's some built in tension so the tonearm doesn't just fall when you loosen the bracket. After raising or lowering the tonearm, retighten the screws evenly, a bit at a time. Avoid overtightening. Be sure to have the tonearm firmly in the tonearm rest while you're adjusting the tonearm height.

SME 309 VTA adjustment bolts

Regards,
Tom