How to increase VM HDD and RAM sizes?

For memory at least, this can be done in the settings for the VM - in 4.3.10 atleast, this can be found under 'System':

You may also want to increase the video memory:

For the hard disk, if you chose 'Dynamically Allocated' it should automatically increase its size up to the fixed size you gave it when you first set up the VM. You may be able to resize it with modifyhd or something else - see here or here. A bit more information on that can be found here. You can view info on the VM's storage under 'Storage' in settings:

sure you can.

To add some more ram to the VM press alt+f2 and type virtualbox.

Select desired VM and got to "Settings" menu. After go to system and on the right you will be able to increase RAM.

It is not so easy to resize HDD, here is a good how-to with screenshots.