Most probably it is not.
WiFi antennas on theese devices can even be SMD only (trying to improve is waste of time), or "copper plate sticker" type, ussualy stickered on the internal back cover.
I've been messing around with the second type on crappy chineese WiFi phone - I've added a tiny connector used in mobilephones and connected simply a piece of coax wire to make a dipole. After few changes signal finally got a bit better, but also because in original it was really poor.
If there is a sticker-type antenna, it is theoretically possible to change antenna quite easy. In practise, you will hardly get it better because you can't just put some wire in and done (well, you can, but it will be like wining a main prize in lotery if it gets better). The wire should have right size, right shape and must be on right place. And milimeters makes a difference there, so have fun
Most likely it can get better only with some kind of external antenna, but you could hardly use your phone as mobile then
Easiest way to tune-it-up could be disconnecting the original sticker and connecting a flexible internal notebook type of antenna, but even that will probably be too big to fit inside - it must not overlap another antenna. And that's not the only rule.
Even if it does not overlap anything, it can interfere with other circuitry or Tx-devices. Bluetooth works on almost the same frequencies as 2.4GHz Wifi, for example. It's a piece of science theese frequencies, actually
I'm absolutely NOT thinking of trying to tune it up on my LG O2x, coz I know it won't be better