For installing custom recovery, your Lenovo A390 must be rooted. If you haven’t rooted it yet, just follow the below instruction. Warning: Make sure to back up your data (contacts, sms, apps, etc.) using apps like Titanium backup before proceeding
Root Lenovo A390
- Download the latest version of Framaroot on to your phone and install it just like any other apk file 
- Run the app and from the dropdown menu list select “Install SuperSU”. 
- To start the root exploits, in the rooting menu select BOROMIR and proceed. Once the process is finished, reboot your device. That’s it. 
Install custom recovery (CWM) on Lenovo A390
- Download CWM recovery.img from here and put it to the root of your SD Card
- Go to Play Store and install the MTK (Mobileuncle MTK Tools) tool, and launch it.
- From the menu, select “Recovery Update”
- The tool will search your SD card for “recovery.img” file. Once it find, select the recovery under “Recovery file in SDCard” and Click “OK”
- It will ask you to reboot into recovery. Click Ok to boot your phone in CWM recovery. [Source]