I am looking to upgrade my BOINC version 4.19 to 4.25, but I am worried I will lose all 17,000 credits my computer has already completed. If I were to uninstall the current version and install the new version will my credits start from zero on this computer?

I am not worried about my total credits overall just the credits for this individual computer.
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You will not lose credits.
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Link to Unofficial Wiki for BOINC, by Paul and Friends

> I am looking to upgrade my BOINC version 4.19 to 4.25, but I am worried I will
> lose all 17,000 credits my computer has already completed. If I were to
> uninstall the current version and install the new version will my credits
> start from zero on this computer?

No, you can even continue to compute the WUs currently assigned to your machine.
Stop the Boinc manager, deinstall 4.19 install 4.25 into same directory - or copy it to another disk if you prefer so.
If you have ATI graphic you should not use the screen saver - there is a risk you'll lose the WU currently being computed - some onchip graphics may also have this problem.

You should also be aware of that the credits claimed by 4.2x are somewhat lower (10-15%)
>
> I am not worried about my total credits overall just the credits for this
> individual computer.
No assigned credits will be lost, as already stated below.

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