How can I remove wheat pasted posters from my wall without damaging the posters?

I recently moved into an old house that has some leftover art from the past tenant. I found some great looking posters wheat pasted to my walls which I would love to keep. The house is old and the walls are made of plaster

On the off chance that you have a particular style of workmanship you're searching for, I could prescribe individual locales where individuals offer prints and blurbs of their fine art.

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