Your PC specs are decent and you really shouldn't be having these problems.

Have a look at your task manager CTRL + Shift + ESC, pay attention to the tabs "Processes" and "Performance", try to identify what programs are using the most system resources and close them if you aren't using them.

A great app for reducing the load on your PC is CCleaner, it has a great suite of tools, specifically Tools > Startup, try to reduce the amount of start up programs to as little as possible.

ProTip: You can disable almost all of the programs in this list.

Running CCleaners "Cleaner" tool will remove a lot of junk files from your computer and free up space on your HDD, which can cause your computer to slow down.

Running the registry cleaner tool is good too, although will have minimal impact of performance.

Make sure you have an anti-virus and that it's up to date, some viruses have been known to use lots of system resources.

Lastly, if you still aren't getting satisfactory performance you can always reset your PC, handly I've created a guide for doing that.

Let me know if this helps.