Jessica's desktop is about eight years old and she has nearly a TB in free space on her hard drive. But she's concerned about the age of her computer. Leo says older computers aren't as slow as newer computers like the old days. So an older computer really isn't that big a deal. The more worrisome thing is the age of your hard drive. They can crash as they get older. So replacing the hard drive will be faster and give new life to your computer. Especially with a solid-state drive or SSD.
If she buys a new computer, will the transfer of the data be a problem? Leo says no. At worst, you'll have to reinstall your applications. But there's a tool that will help you transfer your data. Having a backup will make it easier. So do one more backup of your current computer hard drive to an external drive and you can then restore the data after upgrading it.
So you don't really need to buy a new computer, just get a new SSD drive. It'll come with a bit for bit copy utility that will enable you to move the data over. Then your old drive can act as a backup. Then you can spend the money on a nicer monitor. Maybe even get more RAM.