How can I clear the cache in OS 10.10.2?

Good Afternoon. I am having issues with OS 10.10.2 I have been alerted to upgrade to 10.10.3, but I think I should first try to clear my cache. My machine has been running more slowly than I am used to. It also takes an unusual amount of time for applications to quit or start or for me to change from one user to another (me or my wife). I have also had it lose wi-fi connection a number of times and yet my iPhone 6 does not lose it. I have tried taking the time to quit out of everything, shut down, and restart, but it only makes a difference for a very short time and then the above referenced issues return. I am using:

Model Name: iMac

Model Identifier: iMac11,2

Processor Name: Intel Core i3

Processor Speed: 3.2 GHz

Number of Processors: 1

Total Number of Cores: 2

L2 Cache (per Core): 256 KB

L3 Cache: 4 MB

Memory: 16 GB

Processor Interconnect Speed: 5.86 GT/s

Boot ROM Version: IM112.0057.B01

SMC Version (system): 1.64f5

I will be grateful for any guidance you can offer. Thank you.