What to say when returning a purchase - Germany

My partner bought a pair of pants for me at SkiLine 24 and I need to exchange them for a different size. Although I understand a lot of German, my speaking skills are still under construction...Can anyone give me a quickie sentence to convey that I need to exchange them>? Any assistance would be greatly appreciated.

Sorry if this is posted in the wrong section.
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Ich möchte die Hose umtauschen. Haben Sie sie auch in Größe (insert desired size here)?

You can also say, Ich habe falsche hose gekauft, ich will es umtauschen.Haben sie vielleicht andere große? then u say the size u want.

If you don't have a receipt try beginning with ' Ich habe die Hose als Geschenk bekommen. Leider passen die nicht, ich möchte umtauschen.'

Thank you all so much, I used an amalgamation of all of these, basically, "Diese Hose passen nicht, Ich mochte sie umtauschen..." and no worries!

Thank you all so much.

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