No. Converting a lower-bitrate file to 320 kbps does not improve its quality — and any site with a '320kbps upscaler' is selling you a bigger copy of the same sound. We build audio tools for a living and would love to tell you otherwise; the physics won't cooperate.
Why it can't work
Lossy encoding (MP3, AAC, OGG) works by permanently discarding the parts of the sound least likely to be heard. That data doesn't hide in the file waiting to be restored — it does not exist anymore. Re-encoding at 320 kbps faithfully preserves everything the 128 kbps file still has, which is exactly a 128 kbps listening experience in a file 2.5× the size.
It's worse than neutral, slightly: every lossy re-encode discards a little more at the margins. Converting 128→320 doesn't audibly damage the file, but it certainly doesn't polish it.
When 320 kbps IS the right choice
Converting from lossless sources — WAV, FLAC, AIFF, a fresh recording. There, 320 kbps (or better, VBR quality 0) genuinely captures effectively everything, because the detail exists in the source to be captured. That's the honest use, and Sonvert's converters do it locally, free, without upload.