iMac cleanup advice

The iMac (21.5-inch, Mid 2011) runs very slow recently after upgrading to macOS High Serria. I did clean up the trash and unused app but there is no dramatical improvement for performance. what should I do?
atc98092 wrote:I think you'd find much better support on a Mac support forum. There aren't that many Mac users here, compared to other OSs.
holdingars wrote:The iMac (21.5-inch, Mid 2011) runs very slow recently after upgrading to macOS High Serria. I did clean up the trash and unused app but there is no dramatical improvement for performance. what should I do?