I've changed my old HDD to a new SDD and I've installed everything from zero. In the old one i had a very good Upload Ratio so downloading anything was a pleasure. Is there any way i can "import" muy stats to the new disk? (copying config files or anything?)
Thanks.

yes. simply copy the tixati install folder from the old drive over to the SSD

The stats shown in the client are just that, client side. If you are on private trackers then changing clients will not change your ratio.

If you are running the portable version then just copy over the whole folder. If you are running a non portable version move the app data as well.  I can't give you specific instructions on how to move app data without knowing what OS you are on.