verb
to exchange (goods), to change (money)
B1
Umtauschen means primarily 'to exchange' (return or swap goods) and 'to change' (money). It is a separable, regular (weak) verb with perfekt umgetauscht and uses haben as auxiliary. Not reflexive; you separate the prefix in main clauses (ich tausche um) and attach it in compounds or perfect (ich habe umgetauscht).
Examples
Sie tauschte das Geschenk um.
She exchanged the gift.
Ich muss das Hemd umtauschen, weil es zu klein ist.
I need to exchange the shirt because it's too small.
Ich habe das Geld umgetauscht.
I exchanged the money.
Details
Mnemonics
Imagine handing a shirt back to a shop and them turning it around on the counter to give you a new one.
Think 'um' like 'around' — you turn the item around to swap it.
Notes
Umtauschen is separable (um|tauschen). In main clauses the prefix 'um' goes to the end (ich tausche um). It is a regular (weak) verb and uses haben in perfect tenses.