Easy way is to use enough force to prise the sideframes apart enough to drop the axle out.
"Proper" way is to gently ease the brake-block assembly upward (compressing the springs) and inward until it pops out...
...catch the springs as they fly away(!) then you can move the sideframe upward and outward so it comes away from the bogie. Best done after removing the bogie from the tender chassis!
The fun bit (of course) is re-assembling and getting the springs back in place! Having just done it after taking these photos, I found the best way is to refit the sideframe, place the springs in their holes in the sideframe, fit the brake block assembly whilst compressing the springs with a knife blade, then tweak to ensure the springs are seated properly on the spigots on the brake block assembly. I expect the folk assembling these tenders at the factory have this down to a fine art!
I have two of these tenders. On the older one the plastic tubes between the half-axles split. Two axles I fixed by binding with wire and gluing, two were replaced with the body of a pen which was just the right size!
