I've currently bootloader 5.5.242 but I read in your tutorial :

"In SD it can be 4 GB to a maximum of 32 GB: If the bootloader is previous than 5.5xxx, change it to to 5.5106 (5.5120 for x00)"

Does that mean it's better if I downgrade bootloader with 0.0001 then install 5.5120 before installation of Nav 9510 ONE y XL X 00 32 MB Ttuser ??