If you have never looked for it in Android, you are not able to select the resolution for ex 1204x768 using the Android graphical user interface (GUI), instead you are able to change the DPI or density of the screen. with the exception of the third and fourth option you will have to root your device.
The easiest way to change the DPI is to download a DPI changer APP. With these apps you have the option to select a pre-configured DPI setting and commit the change. Some of these APPS claim to change the resolution with out rebooting your device. Other APPS require you to reboot your device before the resolution change takes effect. Either way you will have to root your device so before trying this make sure your phone, tablet or other Android device is rooted. The reason the device must be rooted is because the file that is altered to change the resolution is located on a locked partition. Without rooting your device the application will not have permission to alter the file, hence will not be able to change the DPI of your screen. Do a search for "DPI Changer" in the Play store to find a DPI APP.
The other option to change your DPI is to edit the build.prop file manually on your android device. Again this will require root because it is located on a locked partition other wise. This is the file that is typically alter by the DPI changer app to modify your resolution. It is just done behind the scenes so you do not need to open the file, find the entry and then modify it. For this option look for a "Build.prop editor" in the Play store to find the appropriate application.
Thanks to XDA forum member HypoTurtle for bringing this option to my attention. If you are familiar with the command line utility ADB, you are able to run a shell using the following not including the quotes "adb shell". This will bring up a shell, or command line interface allowing you to type commands that will be executed on your Android device. Its similar to running SSH on a UNIX system only you have more access to your Android device i.e. pushing and pulling files. Once you have the shell you may execute the following commands to change your DPI or resolution.
For Remix OS you can also add a kernel option "DPI=" putting the DPI you desire after the = symbol. This will adjust the resolution so you are able to see or fit more on your screen depending on the resolution of your monitor. For me this was a life saver because my screen was so tiny, resolution of 3840x2160 I could not see anything. After adding the DPI kernel option my screen was a lower resolution making the objects on the screen larger so they could be viewed. You will need to edit the grub bootloader or whatever bootloader you are using to make this change.