Do you Know guys why all NOKIA phone 3rd edition become very slow?

Here you are,
There is a bug in the firmware and unfortunately it haven't been fixed even after the latest firmware update,
which is :
Each time you run an application in your phone and especially (Gallery, Contact List, dialed Nos, or most of original applications that they still in cash memory and they are still in the background consuming phone memory even if you close them from where you ran them.
The only way to refresh phone memory to come back free is to have one of browser application that give you access to phone drives (C: Disk, D: RAM, E: MEM CARD, and Z: ROM.)under this list of drive if you are using ActiveFile (software, or any browsing software that give you Processes and tasks.
Just Access the Task and do end task, or kill the task for any running application you know that you close it.
Go back to check D Drive and by each time you kill/end task you see the drive space growing which means more memory space and more speed for you phone.