As long as the SSD is the same size or larger than the HDD, you can use the Disks application to create an image.
Open the Disks application, select the drive you want to create an image of.
In the upper-right, you'll see a 'three-vertical-dots' button. Click that and select "Create Disk Image". Select somewhere that's not on the disk being backed up to save the .IMG file.
Now that the .IMG file is created, plug in your SSD and in the Disks application, select the SSD, select the 'three-vertical-dots' button, then select "Restore Disk Image". Navigate to the .IMG file you just made, then set it to running.
When it's done, the SSD will be an exact duplicate copy of the HDD. Then it's just a matter of getting it to boot from the SSD, which you'd do in the BIOS / UEFI.
You likely would want to do all of this from the Zorin OS Boot USB stick, so no files on the HDD are in use. That way, you can create the .IMG file (saving it to a third drive), shut down the machine, unplug the HDD, plug in the SSD, boot the Zorin OS Boot USB stick again, then restore that .IMG file to the new SSD.
Then you'd shut down again, and on the next startup, go into the BIOS / UEFI to set it so the SSD boots.
I wrote a script that backs up a drive to a .IMG file and compresses it... basically, it chains dd to 7z:
clear; echo "NOTE: THIS SHOULD ONLY BE RUN WHEN BOOTED FROM THE ZORIN OS USB STICK AND WITH ALL SOURCE DRIVE PARTITIONS UNMOUNTED!"; echo "$(read -r -p "Press Enter to continue..." key)"; clear; echo "Are you certain that all partitions on the source drive are unmounted?\nStarting Disks application... please wait..."; sleep 3; gnome-disks; clear; echo "$(read -r -p "Press Enter to continue..." key)"; clear; echo "Backing up. Please wait...\nEnter source drive (for instance: sda)..."; read source; echo "Enter destination path (for instance: /media/zorin/Storage/) ONLY... file is automatically named."; read destination; clear; echo "Backing up. Please wait..."; sudo dd if="/dev/"$source ibs=512 obs=512 iflag=fullblock,nonblock,noatime oflag=direct conv=noerror status=progress | sudo 7z a -mx9 -bd -si -mmt12 "$destination""$source""""$(date +%Y-%m-%d%H%M).img.7z"; echo "$(read -r -p "Backup complete. Press Enter to exit..." key)"; exit