rolling back installed AMD graphics

Question

My laptop is R510IU-LSFX with AMD Radeon R7 Graphics Processor. I installed AMD graphic drivers for ubuntu 18.04 LTS according to this link

As it is mentioned in the link, I performed these commands in sequence:

sudo add-apt-repository ppa:kisak/kisak-mesa

sudo dpkg --add-architecture i386

sudo apt update && sudo apt upgrade

sudo apt install libgl1-mesa-glx:i386 libgl1-mesa-dri:i386

sudo apt install mesa-vulkan-drivers mesa-vulkan-drivers:i386

Note: I got some "package not found or not downloaded" errors during these commands.(but ignored)

then I rebooted to apply changes. but I faced the screen below which the system was stuck there for hours: stuck screen

I fortunately solved it by passing 'nomodeset' as command but when I entered Desktop, everything was big. Here are the things I have done but couldn't solve:

• "Software and updates" --> "Additional Drivers": but no additional drivers available.

• settings --> devices --> display: the only resolution available is 800*600

• i tried the solutions in this question but i face the response below on first command:

Reading package lists... Done

Building dependency tree Reading state information... Done

Note, selecting 'fglrx-pxpress' for regex 'fglrx.*'

Note, selecting 'fglrx-updates-core' for regex 'fglrx.*'

Note, selecting 'fglrx-glx' for regex 'fglrx.*'

Package 'fglrx-updates-core' is not installed, so not removed

Package 'fglrx-glx' is not installed, so not removed

E: Unable to locate package fglrx-amdcccle.*

E: Couldn't find any package by glob 'fglrx-amdcccle.*'

E: Couldn't find any package by regex 'fglrx-amdcccle.*'

How can i roll back the changes or get the optimal resolution??

I would really really appreciate your help.

Looking for your solutions.