Elementary OS is slow and unstable

How to safely remove 5.7.8 kernel

cd /var/lib/initramfs-tools/
sudo rm -rf 5.7.8
cd /boot
sudo apt --purge remove linux-image-5.7.8
sudo rm -f config-5.7.8
sudo rm -f initrd.img-5.7.8
sudo rm -f System.map-5.7.8
sudo rm -f vmlinuz-5.7.8
sudo update-initramfs -u -k all
sudo update-grub
sudo systemctl reboot
sudo apt update && sudo apt upgrade && sudo apt dist-upgrade && sudo apt autoremove && sudo apt autoclean
sudo purge-old-kernels
sudo apt --purge autoremove
sudo update-initramfs -u -k all
sudo update-grub
sudo systemctl reboot

How to install Realtek Wi-Fi drivers manually

Type in terminal:

cd
mkdir /home/username/Downloads/realtek
cd /home/username/Downloads/realtek
sudo apt-get install --reinstall git dkms build-essential linux-headers-5.3.0-62
git clone https://github.com/tomaspinho/rtl8821ce
cd rtl8821ce
sudo chmod +x dkms-install.sh
sudo chmod +x dkms-remove.sh

Type to install:

cd /home/username/Downloads/realtek/rtl8821ce
sudo ./dkms-install.sh

Type to remove if you will have to remove it after the reboot.

cd /home/username/Downloads/realtek/rtl8821ce
sudo ./dkms-remove.sh

How to install Realtek firmware

Make directory for Realtek firmware

mkdir /home/username/Downloads/rtl

Enter directory for Realtek firmware

cd /home/username/Downloads/rtl

Download Realtek firmware

wget https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/rtl_nic/rtl8168fp-3.fw
wget https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/rtl_nic/rtl8125a-3.fw

Copy Realtek firmware to proper firmware directory in system

sudo cp rtl8168fp-3.fw /lib/firmware/rtl_nic 
sudo cp rtl8125a-3.fw /lib/firmware/rtl_nic

Update initramfs:

sudo update-initramfs -c -k 5.7.8

update GRUB:

sudo update-grub

check kernel version after reboot:

uname -mrs

check errors after reboot:

sudo journalctl -xb
sudo dmesg

How to upgrade Elementary OS to the newest kernel.

Install necessary packages

sudo apt-get install build-essential libncurses-dev bison flex libssl-dev libelf-dev

Make directory for kernel

sudo mkdir /home/yourusername/Downloads/kernel

Download kernel 5.7.8

cd /home/username/Downloads/kernel
wget https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.7.8.tar.xz
tar -xf linux-5.7.8.tar.xz
cd linux-5.7.8
cp -v /boot/config-$(uname -r) .config
make menuconfig

Save config and then exit. Use tab button to select first the save button, then, OK, then Exit, and once again exit.

use 4 core/thread - if your processor have 4 cores

make -j 4

use 8 core/thread - if your processor have 8 cores

make -j 8

Type in terminal

sudo make modules_install 
sudo make install 
sudo update-initramfs -c -k 5.7.8

ignore these errors below, just because those three bin files are not made yet

W: Possible missing firmware /lib/firmware/amdgpu/navi12_ta.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi10_mes.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_dmcu.bin for module amdgpu

Update grub entries and restart the computer

sudo update-grub
sudo reboot

After restart open terminal and type, to check the kernel version:

uname -mrs

to check errors after reboot:

sudo journalctl -xb
sudo dmesg