Your PRL will not help you get better LTE reception. It effects voice and 3G service. Updating your Prl will reset your radio and may grab a better signal when it restarts. Digiblur has a informative article about it on the front page.
As for trying to force LTE, you can set you preferred network to LTE. Dial *#*#4636#*#* in your dialer and click Phone Information. Scroll down to preferred network type and change it to LTE only. Just to let you know, this will not guarantee a LTE connection and may will drop to 1xRTT