I just lift them up off the windshield until they stop (as if you were wiping the windshield with windex), then I wiggle them a bit while pulling up until they come off the splined base. It takes about 2 seconds per side.
When the arm is at rest on the windshield, there is a little 'extension' underneath it that locks under the base.
Yours may be seized from being on there for a long time, so a rust penetrant may help. Good luck!
Michael
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