Hi Netroxy, Welcome to the Unreal Engine 
I understand what it’s like to be new to the toolset, but the answerhub is supposed to be a place for people to find answers to questions when they can’t find the answer elsewhere. Your question is something that you can find an answer to with a simple google search or by looking up tutorials on youtube. For example: https://www.youtube.com/results?search_query=UE4+change+first+person+arms&page=&utm_source=opensearch
Do some searching on your own for the basics and post here when you need some more difficult questions answered. If you want some suggestions for places to learn the engine, I recommend:
The official YT channel - https://www.youtube.com/user/UnrealDevelopmentKit
Tesla Dev - https://www.youtube.com/user/TeslaUE4
Matthew Wadstein - https://www.youtube.com/channel/UCOVfF7PfLbRdVEm0hONTrNQ