Smartphone owners are no strangers to upgrading to the latest, greatest model. In fact, according to phone recycling site Mazuma Mobile, over 20 million handsets will be upgraded in the UK this year. Furthermore, each household has on average four unused phones languishing in the backs of cupboards, which amounts to some 50 million phones. Many of these end-up getting dumped, which is having a negative effect on the environment.

Rather than letting these smartphones gather dust, it's worth considering selling them to a recycling firm, which offers you cash for your old handset and then passes the redundant devices on for use in developing nations.

However, rather than heading straight to one phone recycling site, a comparison site that trawls a number of mobile recycling sites, such as PC Advisor's own mobile recycling comparison site, will help you see just who's offering the best deal for your handset

It's worth noting that before you sell your smartphone, you need to make sure all of your data has been removed. The best way to remove content is to implement a factory reset, but you'll also need to remove your SIM card and memory crd, if you have one installed in the device.

Here's how to sell your phone online.

Step one
Start by visiting a mobile recycling compare site such as PC Advisor's own site . You can either enter the phone make and model in the search box at the top of the page or browse the list of most popular devices and select the one you want to sell.

Step two
Once you've selected the device you want to sell, a list of the recycling sites and how much they're offering will be displayed on your screen. Decide which service you want to use and then press the Sell now button located to the far right-hand side of the service.

Step three
You'll be automatically redirected to the site, in our case it was Mazuma . You'll be asked to confirm the make and model of the handset and whether it's in working or non-working order.

Step four
Next, you'll be asked to select how you want to receive the cash in return for the old mobile phone. This can be in the form of a cheque, a same day bank transfer or vouchers for high-street retailers.

Step five
Now enter the IMEI number of the handset you're recycling. In some devices this is located beneath the battery, or near the SIM holder. Alternatively, press *#06# on your phone and the 15 digit number will be displayed.

Step six
Press Sell this mobile. You'll be presented with a summary of the details you've entered, which you should check are correct and then press Place this sell order.

Step seven
If you've already sold a handset via this recycling service, you simply have to enter your username and password. Alternatively, if you're new to the service, enter your contact details and select a password then press Create my account.

Step eight
Next you'll be asked to confirm the order once again and enter your bank details, if you've selected a same day transfer. Now a sales pack that contains everything you need to sell the phone, will be posted to you, although you can also print one from the website yourself. The sales pack includes a confirmation of the sale, a delivery note, a freepost bag and posting instructions.

It's worth noting that while the freepost bag included lets you return the phone at no charge, if it is lost in the post, you'll receive limited compensation, and then that's only if you took the bag to your local post office and obtained a proof of posting receipt (It can also be popped in a post box). We recommend you take the bag to the post office and use Royal Mail's Special Delivery service, which will see you incurring a cost, but offers up to £500 in compensation should your device not arrive.

Step nine
Once you've post your device just sit and wait and the recycling firm will issue your cheque, vouchers or bank transfer on the day it receives the handset.