Hi szeresz and welcome.

Sony do not offer upgrades and trying to get someone to add bluetooth internally is not really cost effective as the cost would be high.

Quite honestly, I don't know if there is space available as none of the early E-Series Vaios had bluetooth installed.   You could ask a local repairer how much it would cost.

If it was me, I would just add a small nano USB bluetooth receiver - these are very cheap and very effective.