Hello Najla Matti, the SSD is more faster than the HDD. When you replace it your laptop will load faster and the programs will run faster. The best brand for SSD is Samsung. The life time of the SSD also is better than HDD.
The main benefit of computer system is it's speed nothing else. Might be you will be agree with me. When you are replacing HDD with a SDD, you will get much better booting time, nice access time and there is no need for disk defragmentation. So, even your older computer can perform better, this is very nice thing. But one thing must be notice that cost difference is quite big. I hope that you will be satisfy.