Looks like it's a cantilever brake on the back, so not straightforward, you can't really use a different wheel size unless you can find a way of sorting out the rear brake. Do you have the fork as well?
@ghettro started
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Looks like it's a cantilever brake on the back, so not straightforward, you can't really use a different wheel size unless you can find a way of sorting out the rear brake. Do you have the fork as well?