Smartphone stuck with no enough memory

Hi there,

I was using my Techno M3 to shoot videos and pictures during a wedding celebration, the device indicated memory full, it started acting so slow until I went home, connected it to a PC and transferred all the videos to my PC, but my phone got stuck on the message that there's is no enough memory,  I have tried restarting the phone but the message is still there, it is making the phone be slow, how do I stop this message? What could be the problem?