Why can't I save apps into my SD-card? I have a problem with my lenovo S750.
When I want to download something the system says: 


  Memory Full, Not enough storage space


It's really frustrating since I cannot use the android at all!  

My phone is rooted, and I already tried to use Clean Master to move all of my apps to the SD-card, but it only moved 5 apps for me, but other than that, there is no apps on the SD-card, only photos and few videos.
The rest is probably still on the internal memory.  


Internal storage is full (1GB)
micro-SD card is half empty(2GB)
phone storage is empty (1.55GB of total 1.64GB free)


Since internal storage is full, no apps will be updated due to lack of storage.

Furthermore, how can I take advantage of the phone storage?
You have to wipe your cache partition. It is the partition where Android stores downloaded .APKs and some other system data and you cannot see it with a file manager.

Step 1

Turn off your Android device. Reboot the phone or tablet into Recovery Mode. The process is specific to the device model. For Lenovo S750:    


Press and hold Volume Up and Power Button at the same time.
Release all buttons when the Lenovo S750 screen flickers and in a few seconds the Recovery screen will appear. 
When the Android image appears press Power shortly


Step 2

Press the “Volume-down” button to scroll to “Wipe Data/Factory Reset.”, select it.

Step 3

Scroll to and select “Wipe Cache Partition.”

Step 4

Highlight and select “Reboot System Now.” The phone restarts.

DO NOT make "Factory reset". You will loose all your data on phone.