You can rectify this all what you require is about 2 hours of time as well as a slow Mac that you already have. So lets start of with the speed up process. But. Before we start I would like to recommend you to book mark this page so that you can use it any time it's required.
To Speed up your Mac. Steps to be followed are:
1) Open your hard drive To use the Mac utility already installed on you Mac
Open >> Applications >> Utilities
2) Now run the Disk Utility
3) Now select the disk
Note: If you are seeing two disks there, you need to run the process for one disk first and then repeat the process for the other disk.
4) Once the disk is selected the next step will be to click on the Repair Disk Permissions
5) If you have two disk listed then you will have to run the Repair Disk Permissions for the second disk too.
6) You are done with it, yes Just need to restart the system and you will find that your Mac running faster.
It may happen that even after following all the steps your Mac is still running slow so in that case:
Delete some stuff from your Mac
Try adding more RAM to your system
Delete large files from the system
- Reclaim you hard drive space
Even then if the Mac is not up to your expectation the Only option will be to go for professional services. Speed Up Mac Software can help you achieve the lost performance of you system.