Write down what you want your computer to do in terms of both applications and performance.
Plus any other requirements you may have: desktop, laptop, whistles and bells ( RGB LED's), multiple drives, audio and video ports, room for growth.
What is your budget for a new computer?
Sometimes you can do things such as replacing HDD's with SSD's or adding RAM to help with performance.
Or use an GPU instead of the motherboard's integrated GPU. Are you able to do the work yourself or have a knowledgeable family member or friend help? Maybe for the cost of a pizza and appropriate beverage.
How much money are you able or willing to spend on upgrading the existing/old computer?
Overall, if the current computer is not capable of running the applications and/or games you have or only runs them with very slow performance then it may be time for a new system.