Go through these steps:

1. Locate Menu User Interface/Views [Setting->Technical->User Interface->Views]

2. Search Login 

3. Edit this template  change the values of redirect form t-att-value="redirect" to "/"

4.  <input type="hidden" name="redirect" value="/"/>

<?xml version="1.0"?>
<t name="Login" t-name="web.login">
            <t t-call="web.login_layout">
                <form class="oe_login_form" role="form" t-attf-action="/web/login{{ '?debug' if debug else '' }}" method="post" onsubmit="this.action = this.action + location.hash">

                    <t t-call="web.database_select"/>

                    <div class="form-group field-login">
                        <label for="login" class="control-label">Email </label>
                        <input type="text" name="login" t-att-value="login" id="login" class="form-control" required="required" autofocus="autofocus"/>
                    </div>

                    <div class="form-group field-password">
                        <label for="password" class="control-label">Password</label>
                        <input type="password" name="password" id="password" class="form-control" required="required" t-att-autofocus="'autofocus' if login else None"/>
                    </div>

                    <p class="alert alert-danger" t-if="error">
                        <t t-esc="error"/>
                    </p>
                    <p class="alert alert-success" t-if="message">
                        <t t-esc="message"/>
                    </p>

                    <input type="hidden" name="redirect" value="/"/>
                    <div class="clearfix oe_login_buttons">
                        <button type="submit" class="btn btn-primary">Log in</button>
                    </div>

                </form>
            </t>
        </t>