wifi is degrade using airport time capsule

Sorry, but that is not enough information in order for us to assist you with potential solution.

• Which exact version of the Time Capsule (TC) to you have?
• What are the make & model of your other networking hardware? Modem, gateway, other routers?
• Has this always been an issue or did it just start happening?
• What are you using to measure Wi-Fi performance to know that it is degraded?
• What have you done, so far, to try to resolve this yourself?

Ok, I see you have a 4th gen. 802.11n Time Capsule.

Anytime you change networking hardware or ISPs, it is always a good idea to perform a complete power recycle of your networking equipment. For details on how to do so, check out the following AirPort User tip. Please post back your results.

Unfortunately, both the 1st & 4th generation Time Capsules have been somewhat problematic. Of those most have been related to failing power supplies.

Most consumer-grade Wi-Fi equipment typically lasts around 5 years. These two generations did not so as well. The 4th generation came out in Jun. 2011 and were discontinued in 2013 ... so it's somewhere in that range.

At this point you may want to consider replacing it.

Not sure why that is happening. Have you also tried to force quit the AirPort Utility?

... or used <Option><Command><esc> to force quit it?