I've just downloaded and installed manjaro cinnamon but my screen is small. i googled and realized that my auto-resize guest display is greyed out. I read some posts on this forum but ive noticed that my os is linux 2.6 /3.x / 4.x(64-bit). can i still correct the problem and make my screen bigger? or i would have to delete and start all over?
You need to install the guest utilities. Please refer to this guide.