Over time your phone will collect excess data that can slow it down. You can clear your cache to help speed your phone back up. Start by opening your Apps and then go to your settings. Under General settings you will find a storage option. From here you can select cache data, then choose okay. You can also follow the link to the LG G2 Sprint troubleshooting page on completing a factory reset.
[[LG G2 Sprint Troubleshooting#Section_Needs_Factory_Reset]]