Is there a way to double all frequencies?
That's typically referred to as "pitch shifting" and it's typically a combination of re-sampling and time stretch/compression. Re-sampling is straight forward but time stretch/compression is a bit more tricky and the best methods depends on the application requirements, the characteristics of the signal and the amount of stretch/compression you'll need. See http://blogs.zynaptiq.com/bernsee/time-pitch-overview/ and https://en.wikipedia.org/wiki/Audio_time-scale/pitch_modification to get started