If you are on the verge of upgrading to Windows 10 then to get the most out of this upgrade you should do a clean install.
There is a method becoming popular on the net where you generate a Genuine Ticket of your existing windows installation and use that to do a clean install of windows 10 on a different partition or on a new hard drive all together. This will not only make your system run like new, but will also save you money in the long run. I just followed this method and did this for a client. This client of mine was spending 4 to 6 hours a day on computer preparing various reports for Auto Appraisals, making his laptop a major tool to accomplish his daily work. I suggested that he do a clean install of Windows 10 on his 2 year old Windows 8 computer on a solid state drive. While these upgrades are not cheap they cost about less than half of a new computer with a solid state drive. I completed this job in about 2 days and the customer was happy to have his laptop performing like new with all of his data transferred, including all of his software like Microsoft Office, email client etc. After about a week of him taking back his machine, he dropped in at the shop just to let me know how happy he was and how much time he was saving due to the improved speed and performance of the laptop.
If you are experiencing a slow computer and it is slowing down your work then it is time to consider this upgrade and you will not regret it.