Question details:

I am now having a internet plan with the company named "unwired", but the speed is too slow (probably the modem's antenna is weak). Can I use another brand of modem (say: D-link) that I still could connect to the unwired internet company. Must i use the unwired modem connect to the unwired ISP, or can I use D-link modem to connect to the unwired ISP?

Answer

You can use other modem but you must check if it has the same technical details.

You could also check this two articles to learn how to increase your signal strength:

Article 1

Article 2