Hi there peter6,
Yeah, you can clone your old HDD onto a new one. No need to reinstall OS.
Most of the HDD manufacturers have their own cloning tools. Some third party ones should do the job as well.
Keep in mind that in case your current drive is in a bad condition, then a clean OS install may be a good idea. If your OS has some issues when installed on the old drive, it would have the same issues on the new one as well.(exact same copy)
Let me know in case you have some more questions,
D_Know_WD