wechseln
to change
To replace something with another thing of the same kind; to exchange it.
Ich muss dringend die Glühbirne im Wohnzimmer wechseln.
I urgently need to change the light bulb in the living room.

to change / switch
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to change
To replace something with another thing of the same kind; to exchange it.
Ich muss dringend die Glühbirne im Wohnzimmer wechseln.
I urgently need to change the light bulb in the living room.

The verb 'wechseln' (to change/switch) belongs to the word family around 'der Wechsel' (change/switch). All meanings have to do with an exchange, a change, or a transition from one state or place to another.
Ein Jobwechsel ist oft eine große Herausforderung.
A job change is often a big challenge.
'Wechseln' (to change/switch) can be used with an accusative object to say WHAT you are exchanging. But it can also stand without an object to describe a transition, often together with prepositions.
Ich muss die Reifen am Auto wechseln.
I need to change the tires on the car.
In the meaning 'austauschen' (to exchange/replace), 'wechseln' (to change) is often combined with everyday things that need to be replaced regularly. Typical are: 'die Reifen wechseln' (to change the tires), 'die Bettwäsche wechseln' (to change the bed linen), or 'die Windeln wechseln' (to change diapers).
Es ist Zeit, die Winterreifen zu wechseln.
It's time to change the winter tires.
When 'wechseln' (to switch) describes a transition, prepositions like 'zu' (to), 'in' (into, with accusative), or 'nach' (to) are often used to indicate the new direction, the new place, or the new topic.
Lass uns das Thema wechseln.
Let's switch topics.
When you exchange money, use the structure 'etwas in etwas wechseln' (to change something into something). The preposition 'in' is used with the accusative here.
Ich möchte 100 Euro in Schweizer Franken wechseln.
I would like to change 100 euros into Swiss francs.
The idiom 'ein paar Worte wechseln' (to exchange a few words) means to have a short conversation. It is often combined with the preposition 'mit' (with) and a person in the dative.
Ich habe auf der Feier nur mit wenigen Leuten ein paar Worte gewechselt.
At the party, I exchanged only a few words with a few people.
to speak
'sprechen' and 'wechseln' can both have to do with a conversation, but only in a fixed expression. 'sprechen' is the normal and general verb when you have a conversation with someone. 'ein paar Worte wechseln' (to exchange a few words) means to speak briefly with someone. This expression often sounds a bit shorter or more casual. So you can almost always say 'mit jemandem sprechen' (to speak with someone), but 'Worte wechseln' is used only when it really means a short conversation.

Vor dem Termin wechseln wir noch ein paar Worte mit dem Kunden.
Before the appointment, we exchange a few words with the client.
Nach dem Unterricht spricht Tom mit der Lehrerin über die Aufgabe.
After class, Tom speaks with the teacher about the assignment.