You've probably noticed the explosion of SSD drives in today's computer market, those little devices that might be small but can potentially increase the speed of your laptop or PC by 10x. They come in various sizes, 128gb, 256gb, 512gb, 1tb, 2tb & 4tb. These little drives vary in price, but are traditionally more expensive than your average HDD. For example, a 512GB one can set you back £50, whereas a 256GB will cost you around £25, you can pick up a 128GB one for a mere £18. If you're looking for a 1TB one, that could set you back £100.
Ultimately, replacing your old HDD with an SSD is the most cost effective way of improving the performance of your laptop. Even upgrading a CPU from i3 - i7 is considered small in comparison to upgrading to SSD. Believe it or not, a laptop with an i7 CPU and a traditional HDD is actually slower than a laptop with a core 2 duo CPU and an SSD drive. That might be difficult to digest, but you have to remember that your laptop is running primarily from the HDD, that is the main source of the OS and files. A slow HDD can impact all areas of performance despite you running an i7 with 16GB RAM.
The best way to upgrade your laptop is to start from scratch, assess the RAM, HDD type, CPU & GPU, then work your way up. For example, a laptop with an i5 cpu with 4gb ram, would benefit from an SSD upgrade, and a memory upgrade to 8GB. Wheres a laptop with an i3 CPU, SSD drive, and 8GB ram, would benefit from a CPU upgrade to i5.
There are free software tools out there such as CPUZ that can help you identify the hardware on your computer, tools like this will make life so much easier. But remember, it isn't all about i3, i5, or i7, don't let them trick you into upgrading on this basis alone. Do your research, look into your laptops spec, and upgrade base on the data you have available on your machines. Again, CPU Z has all you need.