Can I use upsampler to update dac?

To answer your question we need to know what dCS products you are talking about. Is it a Vivaldi Upsampler and other dCS Vivaldi components or is it a legacy dCS upsampler and other devices or a mixture of the two?

If it is all Vivaldi then you use Mosaic to update:

Note: Before updating always switch off the device to be updated by the rear panel power switch , leave it a minute or two then switch back on and carry out the update process.

You can also check on the latest firmware/software versions here:

https://dcsaudio.com/documentation