This trick is for stock Lollipop rom .
If you've E signal you can force the phone to connect to H, H+ or even LTE (probably only for short time). (probably also work from H to LTE).
1. Go into settings
2. Tap "more" at wireless and connections.
3. Tap mobile networks
4. Tap network operators and tap "OK" (data network will temporarily be disabled until networks are scanned)
5. Check the networks list for your carriers networks, if you're lucky you'll find a more fast network for your current area. Then tap the fastest network to try connecting, if it can't connect to the fastest, it'll connect to the least fastest.
##You can attempt this anytime you like to try to connect to a better network, LTE networks might not stick long if the signal is weak, but you could just do it again.##
##If you loose the signal after a while, it might happen that you're getting connected to a slower network again. Meaning you can then again follow the instructions to gain a better network##
If you've E signal you can force the phone to connect to H, H+ or even LTE (probably only for short time). (probably also work from H to LTE).
1. Go into settings
2. Tap "more" at wireless and connections.
3. Tap mobile networks
4. Tap network operators and tap "OK" (data network will temporarily be disabled until networks are scanned)
5. Check the networks list for your carriers networks, if you're lucky you'll find a more fast network for your current area. Then tap the fastest network to try connecting, if it can't connect to the fastest, it'll connect to the least fastest.
##You can attempt this anytime you like to try to connect to a better network, LTE networks might not stick long if the signal is weak, but you could just do it again.##
##If you loose the signal after a while, it might happen that you're getting connected to a slower network again. Meaning you can then again follow the instructions to gain a better network##
xda-developers