I am a bit fogged.

毕竟是词组,没有算不算,但作用相当于副词.
不能那样改.
下面是二者用法:
1.a bit和a little都表示“稍微”、“有点”之意,都可作程度副词,修饰动词、形容词(包括形容词化的现在分词和过去分词)、副词、比较级.在肯定句中可以互换.例如:
Will you please turn down the radio a bit/a little?(修饰动词)
She’s a bit/a little afraid of the teacher.(修饰形容词)
The patient feels a bit/a little better to-day.(修饰比较级)
He did his homework a bit/a little care-lessly.(修饰副词)
2.a bit和a little都有some“一些”之意,后接不可数名词.例如:
I’ve got only a little/a bit of money with me today.I’m afraid I can’t help you.
3.for a bit和for a little意思相同,相当于for a while或for a short time,可互换.例如:
I’m going to sleep for a bit/a little.
Let’s rest for a bit/a little.
II.不同之处
1.a little可用作形容词,直接修饰不可数名词;而a bit不能用作形容词,修饰名词时,其后须加上of,构成“a bit of+n.”结构.例如:
Please give me a bit of paper.
He knows a bit of French.
但是,当a little修饰的名词前有this,that以及所有格等限定词时,也要用a little of结构.例如:
I want to drink a little of that wine.
2.a bit可构成“a bit of+不定冠词+名词”,而a little则不能.例如:
I’m afraid your friend is a bit of a thief.
3.a bit和a little的否定式意义正好相反.not a bit=not at all,意为“毫不”;而not a lit-tle=very much,意为“非常”,“很”.例如:
He is not a bit tired.他一点不累.
He is not a little tired.他很累.