@jaime-o Although the subject to be related, the ideal is not "dig out" an old topic that was "stopped". Regardless, yes, it is possible to back up a 32GB card to a 64GB card. However, depending on the tool you use, the 64gb card can be only 32gb visible and the rest "unallocated", which is easy to solve: just use a tool to expand the size of the SHARE partition, for that partition to use all available space. (using gparted from linux is a great option, but some applications for windows, specific to partition HD, also work). (If you are using windows, you can use "SD Memory Card Formatter" to format the card, "win32-disk-imager" to copy the image and the same program to write to the new SD card, or "RUFUS", and if necessary, the "MiniTool Partition Wizard" to expand the SHARE partition after the backup.)
Please open a new topic, specify as much information as possible: If you are using Rpi0,1,2 or 3 (since you are talking about an SD card), which are the cards you are using (which should be original , and class 10), what is going wrong exactly, etc.