Can I install x86 later update it to x64 on my x64 OS ?
It isn't possible to in-place upgrade a 32 bit operating system to 64 bit. A clean installation would be necessary. Regardless the install media will not fit on a 4gB USB. I'd suggest closing thing one by marking answer and open a new thread about the new repair topic.
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and Accept as answer
if the reply is helpful--