Image and font storage and access

I now use LVGL 7.4, using the MCU is NXP MXRT1011, now use the UI images, fonts, and stored in the flash program, download the program is very big, every time takes time, and now want to separate the program, UI and font download to flash the designated area respectively, and then you just need to download the program, would you please tell me why I should turn images and font format, using what tools transformation, how to access these images and fonts