Hi @shishir8-
Yes, this is possible. A "class upgrade" from Zurich to Interlaken Ost costs around 53* Swiss Francs, from Zurich to Wengen 59* Swiss francs and only from Interlaken Ost to Wengen 6* swiss francs. In my opinion, only the upgrade between Interlaken Ost an Wengen is the money not worth, because in the last train between Lauterbrunnen and Wengen, there is no 1st class.
I would recommend you a) an upgrade for the whole route from Zurich to Wengen oder b) from Zurich to Interlaken Ost
Here is a hint for you: Take a look for the IC81 train. This train is operated directly from Zurich (and Zurich airport) to Interlaken ost, without a change.
You can book the upgrade in the SBB App or here: https://www.sbb.ch/en/travelcards-and-tickets/tickets-for-switzerland/class-upgrades-supersaver-clas...
* Difference between "class upgrade" and "supersaver class upgrade": The "class upgrade" is valid on all trains, but more expensive. The "supersaver class upgrade" is only valid on a specific train (indicated on the ticket, but the ticket is cheapter).
I wish you a nice stay in Switzerland.
LG, uebe
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