Hi,
Your question is too general in nature.
A lot of laptops can be upgraded but it can vary as to what and how far, even in the same model range.
Usually the RAM can be upgraded but again this can vary as to what is the maximum amount of RAM that is supported.
With the CPU as it is hard mounted onto the motherboard usually it cannot be upgraded without changing the motherboard.
You may be better off viewing the specifications for the particular models that you're interested in to see what is available to be done by way of upgrading to futureproof them.
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