Complex sentence: Thomas Rigge, a doctor of physick (sic) from Bristol, agreed to take over the mortgage and he repaid Edward Forward his £3000, at the same time increasing the mortgage to £3150.
Split into simpler sentences: Thomas Rigge, a doctor of physick (sic), from Bristol, agreed to take over the mortgage and he repaid Edward Forward his £3000. At the same time increasing the mortgage to £3150.