The image file size in the original logo you've supplied above is only 9.51KB. I suspect it has been highly compressed professionally because when opened in MS Paint the quality seems quite good. Usually Garmin logo images are very much bigger, in the 100's of KBs usually.

Graphics manipulation is not something i know much about. I'm aware there are free online compression tools available, however afaik when using any of them to compress a file the resolution quality reduces in proportion if you maintain picture size, in this case 800x480x32 pixels. I think you'd have to use a paid software program to get such a huge file size reduction (down to ~10KB from 300/400/500KB) and still have acceptable quality. This is the BMW image reduced from 562KB to 26.7KB using a free online tool:
Spoiler: Click

800x480x32 min

I'd think if the already reduced image above was further reduced by another ~65% using a free tool to get it down to the same size as your original Garmin PNG that the quality would be terrible.