First of all, you should find the actual location of the certificates. You can open your nginx or apache configuration to see the location:

cat /etc/nginx/sites-enabled/divbyte.com
...
 ssl_certificate /etc/letsencrypt/live/divbyte.com/fullchain.pem; # managed by Certbot
 ssl_certificate_key /etc/letsencrypt/live/divbyte.com/privkey.pem; # managed by Certbot
...

But this is not the actual place where certificates are located. These are symlinks, to see the actual location you should execute the following command:

sudo ls -l /etc/letsencrypt/live/divbyte.com
total 0
lrwxrwxrwx 1 root root 46 Mar 25 13:23 cert.pem -> /etc/letsencrypt/archive/divbyte.com/cert2.pem
lrwxrwxrwx 1 root root 47 Mar 25 13:24 chain.pem -> /etc/letsencrypt/archive/divbyte.com/chain2.pem
lrwxrwxrwx 1 root root 51 Mar 25 13:24 fullchain.pem -> /etc/letsencrypt/archive/divbyte.com/fullchain2.pem
lrwxrwxrwx 1 root root 49 Mar 25 13:24 privkey.pem -> /etc/letsencrypt/archive/divbyte.com/privkey2.pem

You also need to archive renewal config for your website. It's located in the /etc/letsencrypt/renewal/<domain>/ folder. To archive all files, run the following:

sudo tar -chvzf certs.tar.gz /etc/letsencrypt/archive/divbyte.com /etc/letsencrypt/renewal/divbyte.com.conf

Now you can copy this archive to the web site location, so you can download it to the new server in the next step:

scp certs.tar.gz admin@sevennet.org:/home/admin/

Replace admin@sevennet.org with the destination server info, where admin is a username and sevennet.org is a target server domain or IP.

This is a really simple step. Log in to the new server and extract the certificates:

ssh admin@sevennet.org

Now you need to extract files to the correct location on the new server. Insite archive we already have the correct folder structure, so you can extract it “as is” if you are in the root folder:

cd /
sudo tar -xvf ~/certs.tar.gz

For the correct work, you need to create symlinks in the live folder for your domain:

sudo ln -s /etc/letsencrypt/archive/divbyte.com/cert2.pem /etc/letsencrypt/live/divbyte.com/cert.pem
sudo ln -s /etc/letsencrypt/archive/divbyte.com/chain2.pem /etc/letsencrypt/live/divbyte.com/chain.pem
sudo ln -s /etc/letsencrypt/archive/divbyte.com/fullchain2.pem /etc/letsencrypt/live/divbyte.com/fullchain.pem
sudo ln -s /etc/letsencrypt/archive/divbyte.com/privkey2.pem /etc/letsencrypt/live/divbyte.com/privkey.pem

Update nginx or apache configuration to use new certificates (for nginx):

 ssl_certificate /etc/letsencrypt/live/divbyte.com/fullchain.pem; # managed by Certbot
 ssl_certificate_key /etc/letsencrypt/live/divbyte.com/privkey.pem; # managed by Certbot

Go to your DNS manager and change the A record, so it is pointing to the new server.

This step is required to successfully run a test renewal:

sudo letsencrypt renew --dry-run

You do not need to modify cron tasks for certbot since it's configured in a way that will renew all certificates:

sudo cat /etc/cron.d/certbot
 
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
 
0 */12 * * * root test -x /usr/bin/certbot -a \! -d /run/systemd/system && perl -e 'sleep int(rand(43200))' && certbot -q renew

That's it, the domain name is pointing to the new server and certificates can be automatically renewed

Now you can remove certificates and renewal config from the old server, execute the following:

rm /etc/letsencrypt/renewal/divbyte.com.conf
rm -rf /etc/letsencrypt/renewal/divbyte.com

Do not forget to change the location (the one you found in the first step)

And now you can update your Nginx or Apache config and remove the SSL/HTTPS configuration section.