In order to change standard VNC screen resolution, please follow this steps:

1. Login to your server via VNC or TightVNC Java Viewer.
2. On top menu click Applications >> System Tools >> Terminal
3. In terminal window, type command:

nano /etc/sysconfig/vncservers

4. with arrow key, scroll down to last line and look for:

VNCSERVERARGS[1]="-geometry 1024x768"

5. Change to your desire screen resolution. Once changed, press Ctrl + o to save your setting and press Ctrl + x to exit editor.

6. After save, in same terminal window type command:

reboot

7. Done.

After server back online (normally within 2 minutes), reconnect your VNC client to get new resolution.