Some thoughts and gotca's
One hopes that the new emmc is blank, sometimes it "helpfully" comes with an android install
If you have another bootable SD and a usb SD card reader it gets a lot easier
(hopefully a usb3 card reader, 3x as fast)
Do be aware, your SD boot is using uboot FROM emmc, you really don't know
just how good the uboot on SD is,,, good/mediocre/bad
mate in reader, plugged into usb,,, some other SD card boot, blank emmc
sudo dd if=/dev/sda of=/dev/emmc bs=1M status=progress
Then check (on emmc) if fstab and extlinux.conf point to right place
cfdisk and resize2fs to expand root fs on emmc
If you want to cover all possibiities , copy 1st 16M from original emmc to ~/Documents on SD card first,
the you have a probably good uboot if the SD uboot is not good,, as so
cd ; cd Documents
sudo dd if=/dev/emmc of=1st-16M.emmc bs=1M count=16
One hopes that the new emmc is blank, sometimes it "helpfully" comes with an android install
If you have another bootable SD and a usb SD card reader it gets a lot easier
(hopefully a usb3 card reader, 3x as fast)
Do be aware, your SD boot is using uboot FROM emmc, you really don't know
just how good the uboot on SD is,,, good/mediocre/bad
mate in reader, plugged into usb,,, some other SD card boot, blank emmc
sudo dd if=/dev/sda of=/dev/emmc bs=1M status=progress
Then check (on emmc) if fstab and extlinux.conf point to right place
cfdisk and resize2fs to expand root fs on emmc
If you want to cover all possibiities , copy 1st 16M from original emmc to ~/Documents on SD card first,
the you have a probably good uboot if the SD uboot is not good,, as so
cd ; cd Documents
sudo dd if=/dev/emmc of=1st-16M.emmc bs=1M count=16