Hello & welcome.....In regards to the speedo / ODO readings, there is a function to change this by pushing the buttons on your instrument cluster to access the set up menu. Anyway i'm not 100% sure on how to do this, but i'm sure that other members on here would know how. Other options may be to try a google search as there are plenty of youtube postings etc for WR250R/X info.
If you get stuck then contact your selling dealer, as this really should have been picked up & sorted during the PD process. They should be able to do it in a few mins while you wait.
Cheers.