I created two WordPress themes.
First for the Desktop and second for tablet/mobile. I want to set on one URL. When the website opens, the theme should change automatically based on resolution.
How to set two different themes on one WordPress? (Desktop vs. Mobile)
To employ two entirely separate themes is a suboptimal architectural approach.
Themes are activated site-wide/globally and not on a per-user basis. You don’t want to change the current theme constantly.
While I personally really dislike this option, WordPress ships with a function that sniffs the UA-String,
wp_is_mobile.This function can be employed to either output alternative markup and/or load an alternative stylesheet (from within the same theme).
Or – and this is my personal choice – familiarize yourself with CSS3 mediaqueries.
For simple, you may try this plugin,
http://wordpress.org/plugins/device-theme-switcher/
See this thres also,
How to detect mobile devices and present them a specific theme?
for more customization have to play with code to manipulate the options table meta values for ‘stylesheet’, ‘template’.