type 5 passwords are really hard to crack, especially since Cisco uses I think the 'salted' version of the hash. That said, if you are willing to dive into some dark hacker cracker stuff, here are two links to scripts you can use (I hope posting those links does not earn me jail time):
Haven't tried it but there seems to be a few methods online
they say this works if password is weak
or another method to bypass it using solarwinds
or through python
In addition to the practical hints of Mark and Georg we should look at some background information:
There is no decryption as the passwords are not encrypted but hashed. Although it's also a cryptographic operation, it's not a reversible encryption but a one-way function. All you can do is to take many different passwords, hash them and compare the result to your given hash-value. The used hash-algorithm with type 5 is salted md5 which can be computed lightning fast on modern computers. If you know that the original password is not too complex and long, it should be possible with the given tools.
The triviality in computing md5-based hashes (and also that there can be collisions) make md5-hashed passwords a bad thing and nowadays (at least in newer IOS) pbkdf2 or scrypt is often used. These are the password-types 8 and 9.
Note that @Karsten Iwen mentions a "salted md5".
Here's a link and a quick summary of what "salting a hash" does: To mitigate the damage that a hash table or a dictionary attack could do, we salt the passwords. According to OWASP Guidelines, a salt is a value generated by a cryptographically secure function that is added to the input of hash functions to create unique hashes for every input, regardless of the input not being unique.
The "salt" added to the hash function differs in each device, making the hash unique.