Glass jug and blade base wont undo to clean it !

SOURCE: Broken glass jug on kitchenaid blender model 5ksb2aer4

Look at the underside of the blade shaft. The metal wing nut on the end of the shaft secures the blade assembly to cream coloured plastic blade base. The wing nut also transmits the drive from the rubber coupling on your blender to the blade shaft. The wing nut has a LEFT HAND thread.
The left hand thread ensures the blade assembly does not unscrew during normal blender use.

Firstly disassemble the blender blade assembly. Place a folded tea towel over the blades and hold the blades firmly. If you do not use a tea towel you may cut yourself.

Grip the wing nut with your other hand and unscrew it CLOCKWISE.
Remove the wing nut. You can now remove the blade from the plastic base.

Put the blade assembly in the new jug and offer up the plastic base from under the jug so that the blade shaft protudes enough for you to install the wing nut.

Screw the wing nut ANTI-CLOCKWISE to secure the blades to the plastic base.

Do not over tighten the wing nut; you may have to replace your jug again at some point.

SOURCE: How to replace glass jug

Watch this video. If your jar has a lid that screws in rather than pushes in you unfortunately have to purchase a new lid, blade, gasket and collar.

SOURCE: I have been given a Kenwood BL300 blender. After

You need to unfasten the white base from the clear jug, then the rotating blade will sit inside the white base, with the blade facing upwards. The white rubber flange goes in next. Then screw the assembled base back into the clear jug. The jug should then fit on to the stand.