Saw the exchange of comments between you and @Firelord. Let me try clarify .
You have a cell phone , call it phone A, which can connect to two networks say WiFi1 and WiFi 2. These networks are registered on phone A so passwords need not be entered.
Let us assume this is at home connected to wifi1 and is unattended
Now you go to work and want the phone A to switch automatically from WiFi 1 to 2. This is what we understand as "remotely" from your question
How do you tell phone A to switch? You have to perform some action. This action is called "trigger" . For example, you have another cell phone B at work or borrow to send SMS or give a can give a "missed call" to phone A.
What phone A does when it receives the trigger (s) are called actions. For the actions to run on phone A, you need to have MacroDroid installed on it. Not required to install on phone B
You may want to have some conditions under which this should work, like time of day, day of week and many more. These are called "constraints". The macro runs only is the constraints are "true". If you don't have any constraint,it will always run when trigger conditions are met
Trigger (s) + Action (s) + Constraint(s) create a macro and MacroDroid helps you create macros
MacroDroid, was recommended by since it is easy to learn (that's why I use it) and the behaviour can be easily customized to get the result you want. Besides,free version allows you to create up to 5 macros and so for the task at hand, free version suffices.
Macro for your requirement would look like this:
Call missed → Select Phone B number
SMS received → SMS from (select phone B) → SMS content (enter any content based on which actions will happen)
In this example I used " switch WiFi"
These triggers work in logical OR, meaning to say that actions will happen when either phone A gets a missed call from phone B or gets a SMS having "switch WiFi"
WiFi configure → Forget Network → WiFi 1
Wifi configure → connect to network → WiFi 2
Time of day → start time (select) → end time (select)
(I chose 9 am to 6 pm)
None (if you leave it blank, it runs always)
Save the macro and ensure it is enabled before testing
Based on clarification but by OP that the device to be controlled has only email option and no SIM, only the trigger would need to be amended, as below:
Incoming Notification → choose mail app or any other app that gives notification like hangouts → Text content contains (enter your selected text trigger)
You may be prompted to enable notification access for MacroDroid. Grant that
Ensure that mail or other app like hangouts has notification enabled
If you want to use mail app
a) You can enter the chosen text in mail header
b) There may be times when multiple mails are received at nearly same time, so the app may miss out on reading the notification. To avoid this, you can consider opening a dedicated mail app for this purpose.
Do not Greenify MacroDroid and exclude it from task killers, if you use them.
Enable MacroDroid in "Auto Protect"(Huawei phones) or "Stamina Mode" (Sony phones or "Power Nap" (Stamina Mode Xposed module for non Sony devices). Also, if you update to Marshmallow in the future, exclude MacroDroid from Doze. Refer this: Is there a way to exclude an app from Doze?
These features prevent app(s) to be active when the device is not awake, conserving battery. May not be pertinent to your phone but adding this as a general precaution.
Enable MacroDroid in accessibility settings and also allow it as device administrator in security settings.
For Lollipop, enable notification access from notification settings