If you upgraded your old osx to new and it is now slow. The best thing to try would be to backup your files to an external source, do a full harddrive wipe/format. Then install from scratch.
Apple provide a really easy way of doing this:
Reboot with Command and R (Recovery menu)
Use Disk Utility here to format the drive.
Enter Recovery Menu again and download the OSX iso over wifi and install it fresh.
Obviously requires a decent internet connection to obtain the ISO.
I only suggest this because traditionally, files orphaned by the retired OS can leave their mark.
If you upgraded your old osx to new and it is now slow. The best thing to try would be to backup your files to an external source, do a full harddrive wipe/format. Then install from scratch.
Apple provide a really easy way of doing this:
Reboot with Command and R (Recovery menu)
Use Disk Utility here to format the drive.
Enter Recovery Menu again and download the OSX iso over wifi and install it fresh.
Obviously requires a decent internet connection to obtain the ISO.
I only suggest this because traditionally, files orphaned by the retired OS can leave their mark.