I'm scrambling through arsenal and the bbb to modify my vehicles and drones, the one thing I can't find is improving sensors. I can upgrade to a bigger sensor but not change the rating?

The book you want is Arsenal for figuring out how to modify your drones. However, the first printing of Arsenal was errata'd in regards to Sensor package modification. If you check out the errata for Arsenal over at the main site, you can see (for free!) the rules for Sensor modification (since it was a whole section they completely rewrote), though if you want the really good stuff, you'll have to drop the cash for Arsenal so you can get the really neato sensors.

thanks man, thats a lot of Errata. almost wish i had waited on buying that book

No problem. Actually if you read that errata closely, it's not that hard to improve the sensor rating on your drones (except maybe microdrones... though if you get the Improved Sensors modification, it's doable.) I have Sensors 6 on all my vehicles and drones just by getting R:6 radars, sonar systems, and radio signal scanners. It's nice to get your Sensors to 6 because that's half of your pool for Gunnery and Perception when you are jumped in.