Screen Res­o­lu­tion Prob­lem in Vir­tu­al­Box, Ubun­tu 14.04 and later

1.UP-DATE
First you have to need Updat­ed Vir­tu­al­Box to lat­est version.
Pleas down­load and install from here

2.INSTALL
Inset Guest Addi­tions CD image in VirtualBOX .

and in Ubun­tu install this app

3. TRY A
If you can’t change res­o­lu­tion try install by ter­mi­nal this
sudo apt-get install virtualbox*

4. TRY B
If you can’t change res­o­lu­tion try check this :
Go to Sys­tem set­tings → Soft­ware and Updates → Addi­tion­al drivers
Use x86 vir­tu­al­iza­tion solu­tions and that restart VirtualBox.