If your IMAC began to work slowly, it may indicate an insufficient amount of free space on the hard disk. To solve this problem, you need to "clean" the IMAC, that is, to free the place.
1
The memory of the disks with the programs that were needed only for their installation are strongly littered. Now they occupy an excess place on the disk without performing any function. To delete them, open the "Download" folder in Finder, in the search box that appears, enter the "disk image". Delete all files with the DMG and ISO extension.
2
Remove unnecessary embeddings of emails. The standard Mail application in OS X saves all viewed attached files into a special folder stored on the hard disk. Already after a couple of months of work in the mail, the folder volume may exceed several GB. To delete them, use the search SPOTLIGHT. Enter the Mail Downloads search box. If this way is not able to delete the data, press simultaneously "SHIFT" + "CMD" + "G" (FINDER function). In the field that appears, enter "~ / library / containers / com.apple.mail / data / library / mail". In the folder that opens, review the information. Save all the necessary, remove the rest.
3
OS X saves many different cache files. You can clear the "cache" through the "~ / library / caches" folder or applying a convenient "Cocktail" command.
4
Make sure that after removing unnecessary programs, there are no different files associated with them. You can delete them using the free "AppTrap" program. It works in the background, activating when removing applications in the basket. In a special window, you will see all the files related to the program deleted. Optionally, they can be deleted or left.
After this cleaning, your iMac will work much easier to work, which will certainly affect its speed.