I would suggest that you lay the plant down (on the grass outside or a large newspaper indoors) and then gently remove the pot from the plant. Fill the new pot with the cactus potting mix using the old pot as a mold inside. Remove the old pot and then gently lift the plant into its new pot supporting it top and bottom. A thick pair of gardening gloves will help.
'Optimism is the faith that leads to achievement' - Helen Keller
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