TD-W8980 Can I convert my device from adsl to vdsl?

Yes and I've used a TD-W8980 on a VDSL connection. If your VDSL connection requires Vectoring you will have to source a vectoring capable Lantiq xDSL firmware file as the one OpenWrt can distibute doesn't include this support - I suggest you peruse this thread for more info if you need this.