How to speed up my iMac after upgrading to Sierra? I have this:


iMac (21.5-inch, Late 2012)
2,7 GHz Intel Core i5
16 GB 1600 MHz DDR3
NVIDIA GeForce GT 640M 512 MB


Some days ago I updated to Sierra 10.12.6, and all my apps. My HD currently have about 350 GB free space.

Still, it runs quite slow after upgrading from El Capitan to Sierra.

Any of you had the same issue? How to solve?
Putting an SSD inside will give the most speed boost possible for general computing. If you have a specific benchmark or measurement you want to optimize, there might be other options. 

Since that’s an internal upgrade, you should consider what value you can recoup selling it used and buy a better / newer used Mac than trying to upgrade internal parts on most iMac. 

Since you have a hard drive, you will get the best performance with a hundred free GB and rebooting once a week or so. Other than that, watching for RAM hogs and keeping browser tabs under control are good tips as well.