How do I change the 64gb memory chip

Chromebooks are somewhat notorious for lack of upgradability, and yours is no exception. 64GB is the largest memory option offered for that laptop, so you're already at the maximum. The eMMC memory used as the 'hard drive' is soldered to the motherboard and is not considered upgradeable. Even if you could find a pin-compatible memory chip replacement that had more storage and were able to successfully unsolder the old chip and replace it, there's no guarantee the operating system would recognize it; that would be a crapshoot as to whether it would or not.

Your only other option is to make use of the microSD card reader; you should be able to add more storage by inserting a card.

@rogersheph53237, Here's what the User Manual for your Chromebook says about the SD card.

Chromebook_Manual_ENG.pdf

=== Memory card slot ===

Use a memory card to transfer data to other devices, such as digital cameras or MP3 players. Memory cards are sold separately. Purchase a memory card with the necessary capacity for the requirement.

This computer supports the following types of memory cards.

Abbreviation Description
micro SD • micro Secure Digital
micro SDHC • micro Secure Digital High Capacity
micro SDXC • micro Secure Digital eXtended Capacity

• Some memory cards may not be fully compatible with the computer. Using an incompatible card may damage the computer or the memory card, or corrupt the data stored in it.
• Use caution to insert the memory card in the indicated direction.
• Store the card separately to prevent losing the card when moving the computer.
• Memory card speeds vary.

Inserting a memory card

1. If a dummy card or a memory card adapter is inserted in the memory card slot, remove it.
2. Insert a memory card into the memory card slot in the indicated direction until it clicks.
3. When a pop-up window appears, select it. The Files app will launch.
4. Click on a file to read the data for the file.

Removing a memory card

Push the card gently until it disengages from the memory card slot. Grasp the end of the card and pull it out of the slot.

• Available data formats depend on the current version of the Chrome operating system.
• Data on the card can be saved in the Downloads folder under → Files.
• The maximum file size will vary depending on Chrome OS.