Stick to your old computer, update it or upgrade to a new system is a personal decision, but more informed you are about the matter will make easier to decide which way to go.
If your computer is freezing or running slowly, it may be having difficulty performing its functions, and this impact your productivity.
Computer need minimum specifications to run specific software and work systems. Sometimes you can find your computer is meeting the minimum specifications to run a system, however having the bare minimum may cause a bit of lag, as well.
Computers have also seen a significant drop price over the past years, the PC has reduced its price for many reasons, but there are 2 main reasons:
Supply and demand since over the years the amount of users as being dramatically increased and the parts have become less and less expensive.
New technology has made easier to produce the parts at a lower cost; Old production technology is more expensive thus producing outdated parts is expensive. This is why buying a new part with greater specifications is cheaper than replacing an old part.
Besides the costs of the parts if you add the cost of professional services updating and old computer that will remain outdated is more expensive and still will be unable to perform as well as a new system.