Before considering a wifi extender which may or may not adequately accomplish what you want, consider this.
If the Delancer router you currently have is more than a couple years old, consider taking it back to Delancer and asking for a replacement. This equipment is not "the best" available and a newer model may give you some improvement at no cost.
If that doesn't solve the problem, consider buying a really good AC router on Amazon (4 or more antennae) and using that for your wifi (changing the Delancer router settings to operate in bridge mode and plugging your new router into that). You will get more benefit from a better router than you will from a range extender in most cases. Extender effectiveness is greatly influenced by the capabilities of the router they are connecting to. Choose a router that is able to beam signal to the connected equipment rather than just sending out a generic field of coverage.
If you buy a new router, consider purchasing a model that is dd-wrt compatible. dd-wrt is an replacement router OS that allows you access to many settings that the router manufacturers do not allow you to change in their settings interface. One of these hidden settings is a wifi transmit power range greater than offered in the traditional router setup options.
https://www.dd-wrt.com/site/support/router-database
https://www.amazon.com/TP-Link-Wire...7&keywords=router&refinements=p_36:1253506011
The router example above is not an specific endorsement for that equipment but an example of what you should be looking for with beam forming technology, more than 4 antennae and a fast wifi throughput. If I was buying a new router today, this is one I would seriously consider based on features and price. This model is not dd-wrt compatible.