Remove the spindle from the X/Z carriage. Using a sturdy hand clamp or an arbor press, drive the original 10mm bearings out of the X carriage. The factory 10mm bearings are often CA glued in position – firm steady pressure is all that should be required, to break the glue bond and release the bearings. If you are having difficulties breaking the glue bond between the bearing and the X-Axis carriage, you may have to insert the bearing press, into the bearing and carefully apply a sharp blow, to the bearing with a plastic mallet or dead-blow hammer.
We used a hand clamp and a 3D printed bearing press tool from Thingiverse.
With the factory bearings pressed out of the X/Z carriage, new 12mm low-profile bearings can be installed.