Ljungman will start work in Kyiv from July 3, it said.
Vacher will return to the IMF's headquarters after four years of work in Ukraine.
Read alsoFinance minister Danyliuk specifies timeframe of new IMF trancheThe current reshuffle is part of usual IMF career rotation policies, the IMF said.
Ljungman is a citizen of Sweden and started to work for the IMF in 2007.
He has a degree in Economics from Uppsala University. Previously, he had worked for the Ministry of Finance of Sweden.