Izzy's comment to the original question is actually correct.
On your phone's dialler, dial
*#*#4636#*#* and open the
Phone information menu.
Set preferred network type setting, you can now select the combination of network types that suits you most.
Unfortunately the list of network types uses fairly confusing abbreviations, I'll try to shed at least some light on it:
- 2G: GSM
- 3G: CDMA, EvDo, TD-SCDMA, UMTS, WCDMA (competing standards used in different countries)
- 4G: LTE
I don't have the first idea what 'Global' and 'unknown' do.
Some entries have additional remarks:
- only: use only this particular standard (d'uh 🙂)
- auto (PRL): when your provider's network is unavailable, use the 'Preferred Roaming List' to determine roaming networks preferred by your provider (e.g. that your provider has partnered with)
- preferred: probably means that other network types are not used unless the preferred are unavailable. This may differ from default behaviour because by default, a 2G network may be used even if a (weaker) 3G or 4G network is available.
Remember the original value, in case you pick one that doesn't work for you.
To downprioritize 2G, you might want to try
LTE/CDMA/UMTS auto (PRL): It covers 4G and most 3G standards, falls back to 2G if nothing else is available, and uses a PRL for roaming.
If you're still frequently stuck in 2G mode because you're moving around in an area where 3G/4G is available, but sketchy (for example if you frequently pass through staircases that block all but 2G), you can completely disable 2G by selecting something like
LTE/TD-SCDMA/UMTS and see if that works for you (depending on which network types are used in your country).